首页 | 官方网站   微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   8428篇
  免费   357篇
  国内免费   96篇
医药卫生   8881篇
  2023年   50篇
  2022年   88篇
  2021年   131篇
  2020年   74篇
  2019年   94篇
  2018年   145篇
  2017年   123篇
  2016年   189篇
  2015年   184篇
  2014年   227篇
  2013年   320篇
  2012年   491篇
  2011年   556篇
  2010年   319篇
  2009年   284篇
  2008年   526篇
  2007年   577篇
  2006年   581篇
  2005年   560篇
  2004年   540篇
  2003年   570篇
  2002年   601篇
  2001年   90篇
  2000年   105篇
  1999年   125篇
  1998年   154篇
  1997年   103篇
  1996年   90篇
  1995年   75篇
  1994年   71篇
  1993年   102篇
  1992年   89篇
  1991年   69篇
  1990年   55篇
  1989年   55篇
  1988年   48篇
  1987年   31篇
  1986年   42篇
  1985年   37篇
  1984年   31篇
  1983年   38篇
  1982年   29篇
  1981年   27篇
  1980年   19篇
  1979年   17篇
  1978年   16篇
  1977年   16篇
  1976年   14篇
  1970年   12篇
  1965年   10篇
排序方式: 共有8881条查询结果,搜索用时 0 毫秒
71.
ObjectiveThis study aimed to compare longitudinal changes in ovarian reserve markers after cesarean section (CS) with and without bilateral salpingectomy (BS).Study designWe prospectively enrolled women >35 weeks’ gestation scheduled for CS alone or CS + BS and obtained blood samples for anti-Müllerian hormone prior to surgery and at 3 and 6 months after surgery. At the 3-month visit, we similarly performed transvaginal ultrasound for antral follicle count.ResultsWe enrolled 50 women; 30 underwent CS only and 20 underwent CS + BS. Although anti-Müllerian hormone level increased over 6 months of follow-up in both groups, no clinically important differences in the geometric mean (interquartile range) (ng/mL) were observed at any timepoint (baseline [0.69 {0.36?1.21} {CS only} vs 0.49 {0.32?2.10} {CS + BS}, p = 0.64]; 3 months [1.35 {0.58?3.13} vs 1.45 {1.04?2.25}, p = 0.79]; and 6 months [1.74 {0.93?4.45} vs 2.60 {1.41?5.10}, p =0.27]). Similarly, we detected no difference in antral follicle count.ConclusionBS at the time of CS does not have a negative impact on ovarian reserve 6 months after surgery.ImplicationWhile our results provide reassuring data that bilateral salpingectomy for permanent contraception at the time of cesarean section does not impact ovarian reserve, longer adequately powered studies are needed.  相似文献   
72.
In order to address the hypothesis that 6-aminochrysene (6-AC)is converted to genotoxic products by cytochrome P450 enzymesvia two activation pathways (N-hydroxylation and epoxidation),the activation of 6-AC and trans-l,2-dihydro-l,2-dihydroxy-6-aminochrysene(6-AC-diol) to genotoxic metabolites was examined in rat andhuman liver microsomal cytochrome P450 enzymes using Salmonellatyphimurium TA1535/pSK1002 and TA1535/pSK1002/pNM12 (NM2009)as tester strains. The latter bacteria, an O-acetyl-transferase-overexpressingstrain, was highly sensitive to metabolites derived from activationof 6-AC, but not those from 6-AC-diol, using liver microsomesfrom phenobarbital-treated rats or a reconstituted monooxygenasesystem containing P4502B1 or -2B2, thus suggesting the rolesof P450 and acetyltransferase systems in the activation process.6-AC-diol, on the other hand, was activated very efficientlyby liver microsomes prepared from ß-naphthoflavone-treatedrats or a reconstituted system containing P4501A1 or -1A2; theactivation reaction is considered to proceed through diol-epoxideformation. The contribution of rat P4501A enzymes towards activationof 6-AC-diol was confirmed by the inhibitory effects on theactivation process of -naphthoflavone, a specific inhibitorof P4501 A-related activities, and antibodies raised againstpurified P4501A1 and -1A2. In humans, P4501A2 was found to bethe major enzyme involved in the activation of 6-AC-diol togenotoxic metabolites while the parent compound 6-AC was activatedmainly by P4503A4. Experiments using recombinant P450 proteinsexpressed in human lymphoblastoid cells lines showed that humanP4501A1 could also activate 6-AC-diol to reactive metabolitesat almost the same rate measured with P4501A2. In addition,P4502B6 was found to efficiently catalyze the activation of6-AC to genotoxic metabolites, and P4503A4 was active in theactivation of 6-AC-diol as well as 6-AC. Addition of purifiedrat epoxide hydrolase to the incubation mixture containing purifiedrat P4501A1 or microsomes expressing human P4501A1 caused inhibitionof activation of 6-AC-diol. These results suggest the existenceof different enzymatic activation pathways for 6-AC and 6-AC-diol.The former carcinogen may be N-hydroxylated principally by P4502Benzymes in rats and P4503A4 and -2B6 in humans and activationto its ultimate metabolites may proceed through esterificationof the N-hydroxy metabolites by an N-acetyltransferase. The6-AC-diol is metabolized to its ultimate diolepoxide productby P4501A enzymes in rat and human liver microsomes. P4503A4(humans) and P4503A2 (rats) may also contribute to some extentin the activation of 6-AC-diol, albeit at lower rates than thoseof P4501A enzymes.  相似文献   
73.
3-Hydroxymethyl-5-aziridinyl-1-methyl-[1H-indole-4,7-dione]-prop-beta-en -alpha-ol (EO9) is a bioreductive anticancer agent active for non-small cell lung cancer (NSCLC) and structurally related to mitomycin C (MMC). DT-diaphorase (DTD) is regarded as a two electron reductase that plays an important role in the biotransformation of MMC to antitumor metabolites. To evaluate the role of DTD as a bioactivator of EO9 in NSCLC cell lines under oxic and hypoxic conditions, we examined the inhibitory effect of dicumarol which was regarded as a selective inhibitor of DTD on the sensitivity to EO9 in vitro. In this study, we used an MMC-resistant NSCLC cell line (PC-9/MC4) which was established from a PC-9 cell line as a parent cell line by continuous exposure to MMC in our laboratory. We reported previously that the subline PC-9/MC4 was 6.7-fold more resistant to MMC than PC-9 with decreased DTD activity. The IC50 value of PC-9 against EO9 was significantly increased by co-incubation with dicumarol under oxic conditions. EO9 was more cytotoxic against PC-9/MC4 than against PC-9 cells and the enhancement was impaired by tempol under hypoxic conditions. These findings suggest a suppressive role of DTD against one-electron reduction pathway in the bioactivation of EO9 under hypoxic conditions and EO9 may be more active against oxygen-deficient solid tumors especially in MMC-resistant NSCLC cells with low levels of DTD activity.  相似文献   
74.
BACKGROUND: In regard to postoperative bleeding, the most important consequence of cardiopulmonary bypass (CPB) is the loss of aggregability. However, the mechanism of platelet aggregation loss during CPB is unclear. Newly developed particle-counting methods that use light scattering can be used to quantify changes in the number of platelet aggregates of different sizes after application of an aggregating stimulus. Using a light-scattering method, we investigated changes in platelet aggregation during cardiac operation. METHODS: Nineteen patients undergoing CPB were evaluated. Blood samples were obtained before the operation, 1 hour after initiation of CPB, at the end of CPB, at the end of the operation, and on day 1 after the operation. Platelet aggregation after stimulation by 2.5 micromol/L adenosine diphosphate and 2.0 microg/mL collagen was determined; small (9 to 25 microm), medium (25 to 50 microm), and large (50 to 70 microm) aggregates were counted. RESULTS: Generation of medium and large aggregates after stimulation with adenosine diphosphate and collagen were significantly decreased with CPB, whereas, in spite of hemodilution, the quantity of the small aggregates was maintained at the elevated level. CONCLUSIONS: These results reflect the fact that CPB does not affect the first phase of aggregation. It suggests that platelet dysfunction associated with CPB is mainly caused by an inhibition in the development of small aggregates into larger aggregates.  相似文献   
75.
Seventeen quaternary protoberberine alkaloids related to berberine 1 were tested for antimalarial activity in vitro against Plasmodium falciparum and structure-activity relationships are proposed. The activity of the protoberberine alkaloids was influenced by the type of the oxygen substituents on rings A, C and D and the position of the oxygen functions on ring D. The position of the oxygen functions on ring D and the type of the oxygen substituents at the C-13 position (ring C) strongly influenced the activity. Shifting the oxygen functions at C-9 and C-10 to C-10 and C-11 on ring D resulted in a significant increase in the activity. Compounds bearing a methylenedioxy function at C-2 and C-3 (ring A) or C-9 and C-10 (ring D) showed higher activity than those which have methoxy groups at the same positions. Introduction of a methoxy group into the C-1 position (ring A) decreased the activity. Replacement of a hydroxy group at C-2 or C-3 (ring A) by a methoxy group led to a reduction in the activity. Displacement of a hydroxy function at C-13 (ring C) by the oxygen substituents such as OMe, OEt, OCOOEt, and OCON(Me)2 reduced the activity. In the same replacement at C-9 (ring D), the activity depended upon the type of the oxygen function. Six protoberberines displayed more potent activity than berberine 1. The activity decreased in the order: 10, 11, 17 and 18 > 7 and 8 > 1.  相似文献   
76.
Summary The erythrocyte band 3 (EPB3) variant, band 3 Memphis (EPB3*Memphis), was detected by immunoblotting with a monoclonal antibody to the 41 kDa cytoplasmic N-terminal domain of band 3 without protease treatment of erythrocytes. EPB3*Memphis was also detected by immunoblotting from 3-month-old bloodstains subjected to -chymotrypsin treatment. A population genetic study using this method indicated that the EPB3 variant would be useful for forensic work in Japan, since the frequency of this variant in Japanese (Wakayama prefecture) is relatively high (0.159).  相似文献   
77.
In this report we describe the surgical details involved in refilling the lenses of 13 rabbit and 3 primate eyes using an inflatable endocapsular balloon to restore accommodation. The procedure involves endocapsular phacoemulsification through a small buttonhole or dumbbell anterior capsulotomy or minicircular capsulotomy and the simultaneous preservation of capsular integrity, including the zonules and ciliary muscles. An inflatable balloon made of thin silicone membrane is then inserted into the empty capsular bag. A liquid silicone polymer is injected into the balloon through a delivery tube, and the empty capsular bag is refilled by the inflated balloon. The procedure was found to be reproducible, and an accommodation of 6 D was confirmed in one primate eye. Capsular opacification occurred, but the proliferation and migration of residual lens epithelial cells could be hindered by abundant refilling. This lens-refilling technique may provide restoration of accommodation in future cataract surgery. Offprint requests to: O. Nishi  相似文献   
78.
To investigate the mechanisms of the peritoneal damage induced by continuous hyperthermic peritoneal perfusion (CHPP), protein and fluid loss during and after CHPP and continuous normothermic peritoneal perfusion (CNPP) was studied. Sixteen patients with advanced gastric cancer underwent peritoneal perfusion therapy with saline solution containing 150 to 300 mg cisplatin and 30 to 60 mg mitomycin C for 60 minutes. The temperature in Douglas' pouch was maintained at 42.0°C in the CHPP group (n= 9) and 37.0°C in the CNPP group (n= 7) during perfusion. No statistical differences were found in patients' characteristics between the groups except the maximum temperature in Douglas' pouch during perfusion (41.6°± 0.4°C and 37.6°± 0.4°C in CHPP and CNPP groups, respectively, p < 0.05). The amount of protein lost into the perfusate was 0.35 ± 0.22 g/kg body weight in the CHPP group and 0.37 ± 0.19 g/kg in the CNPP group, showing no significant difference. On the day of surgery, there was no significant difference in the amount of protein and fluid lost through the abdominal drains between the CHPP group (27.9 ± 24.6 mg/kg/hr and 0.94 ± 0.63 ml/kg/hr, respectively) and the CNPP group (25.9 ± 8.6 mg/kg/hr and 1.03 ± 0.31 ml/kg/hr, respectively). We could not find any significant differences in postoperative protein and fluid loss between the groups on the following 3 days either. We conclude that the peritoneal damage by CHPP is not caused by the hyperthermia but by the peritoneal perfusion with saline solution containing anticancer drugs.  相似文献   
79.
(-)-Verbenone, a monoterpene bicyclic ketone, is a component of the essential oil from rosemary species such as Rosmarinus officinalis L., Verbena triphylla, and Eucalyptus globulus and is used for an herb tea, a spice, and a perfume. In this study, (-)-verbenone was found to be converted to 10-hydroxyverbenone by rat and human liver microsomal cytochrome p450 (p450) enzymes. The product formation was determined by high-performance liquid chromatography with UV detection at 251 nm. There was a good correlation between activities of coumarin 7-hydroxylation and (-)-verbenone 10-hydroxylation catalyzed by liver microsomes of 16 human samples, indicating that CYP2A6 is a principal enzyme in (-)-verbenone 10-hydroxylation in humans. Human recombinant CYP2A6 and CYP2B6 catalyzed (-)verbenone 10-hydroxylation at Vmax values of 15 and 21 nmol/min/nmol p450 with apparent Km values of 16 and 91 microM, respectively. In contrast, rat CYP2A1 and 2A2 did not catalyze (-)-verbenone 10-hydroxylation at all, suggesting that there were species-related differences in the catalytic properties of human and rat CYP2A enzymes in the metabolism of (-)-verbenone. In the rat, recombinant CYP2C11, CYP2B1, and CYP3A2 catalyzed (-)-verbenone 10-hydroxylation with Vmax and Km ratios (ml/min/nmol p450) of 0.73, 0.20, and 0.03, respectively. Male-specific CYP2C11 was a major enzyme in (-)-verbenone 10-hydroxylation by untreated rat livers, and CYP2B1 catalyzed this reaction in liver microsomes of phenobarbital-treated rats. Rat CYP2C12, a female-specific enzyme, did not catalyze (-)verbenone 10-hydroxylation. These results suggest that human CYP2A6 and rat CYP2C11 are the major catalysts in the metabolism of (-)-verbenone by liver microsomes and that there are species-related differences in human and rat CYP2A enzymes and sex-related differences in male and female rats in the metabolism of (-)-verbenone.  相似文献   
80.
PURPOSE: The influence of androgen deprivation therapy on dihydrotestosterone levels in the prostatic tissue is not clearly known. Changes in dihydrotestosterone levels in the prostatic tissue during androgen deprivation therapy in the same patients have not been reported. We analyzed dihydrotestosterone levels in prostatic tissue before and after androgen deprivation therapy. EXPERIMENTAL DESIGN: A total of 103 patients who were suspected of having prostate cancer underwent prostatic biopsy. Sixty-nine patients were diagnosed as having prostate cancer whereas the remaining 34 were negative. Serum samples were collected before biopsy or prostatectomy. Dihydrotestosterone levels in prostatic tissue and serum were analyzed using liquid chromatography/electrospray ionization-mass spectrometry after polar derivatization. In 30 of the patients with prostate cancer, dihydrotestosterone levels in prostatic tissue were determined by performing rebiopsy or with prostate tissues excised after 6 months on androgen deprivation therapy with castration and flutamide. RESULTS: Dihydrotestosterone levels in prostate tissue after androgen deprivation therapy remained at approximately 25% of the amount measured before androgen deprivation therapy. Dihydrotestosterone levels in serum decreased to approximately 7.5% after androgen deprivation therapy. The level of dihydrotestosterone in prostatic tissue before androgen deprivation therapy was not correlated with the serum level of testosterone. Serum levels of adrenal androgens were reduced to approximately 60% after androgen deprivation therapy. CONCLUSIONS: The source of dihydrotestosterone in prostatic tissue after androgen deprivation therapy involves intracrine production within the prostate, converting adrenal androgens to dihydrotestosterone. Dihydrotestosterone still remaining in prostate tissue after androgen deprivation therapy may require new therapies such as treatment with a combination of 5alpha-reductase inhibitors and antiandrogens, as well as castration.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号-23

京公网安备 11010802026262号