全文获取类型
收费全文 | 4402篇 |
免费 | 107篇 |
国内免费 | 10篇 |
学科分类
工业技术 | 4519篇 |
出版年
2022年 | 24篇 |
2021年 | 47篇 |
2020年 | 23篇 |
2019年 | 53篇 |
2018年 | 50篇 |
2017年 | 53篇 |
2016年 | 70篇 |
2015年 | 35篇 |
2014年 | 62篇 |
2013年 | 163篇 |
2012年 | 85篇 |
2011年 | 117篇 |
2010年 | 101篇 |
2009年 | 92篇 |
2008年 | 131篇 |
2007年 | 111篇 |
2006年 | 85篇 |
2005年 | 79篇 |
2004年 | 63篇 |
2003年 | 69篇 |
2002年 | 63篇 |
2001年 | 83篇 |
2000年 | 60篇 |
1999年 | 110篇 |
1998年 | 610篇 |
1997年 | 361篇 |
1996年 | 232篇 |
1995年 | 128篇 |
1994年 | 149篇 |
1993年 | 143篇 |
1992年 | 47篇 |
1991年 | 44篇 |
1990年 | 56篇 |
1989年 | 60篇 |
1988年 | 63篇 |
1987年 | 54篇 |
1986年 | 49篇 |
1985年 | 65篇 |
1984年 | 33篇 |
1983年 | 34篇 |
1982年 | 31篇 |
1981年 | 35篇 |
1980年 | 42篇 |
1979年 | 25篇 |
1978年 | 37篇 |
1977年 | 65篇 |
1976年 | 135篇 |
1975年 | 39篇 |
1974年 | 14篇 |
1973年 | 17篇 |
排序方式: 共有4519条查询结果,搜索用时 0 毫秒
1.
Comparison of two methods of surfactant administration and the effect on dosing-associated hypoxemia
M Nelson JJ Nicks MA Becker LA Vrlenich V Bhatt-Mehta RE Schumacher 《Canadian Metallurgical Quarterly》1997,17(6):450-454
OBJECTIVE: The purpose of our study was to test the hypothesis that surfactant dosing through a proximal sideport adapter on an endotracheal tube leads to more dosing-associated hypoxemia compared with a method of dosing that uses a double-lumen endotracheal tube. STUDY DESIGN: Using adequate sample size to compare significant changes in O2 saturation (power > 0.8, alpha < 0.05) we enrolled 36 infants with respiratory distress syndrome in this randomized trial. A 10% change in O2 saturation was considered clinically significant. Nineteen infants received 38 doses of surfactant through the sideport adapter. Seventeen infants received 31 doses of surfactant through the nonventilation lumen of a double-lumen endotracheal tube. Two main outcome measures were assessed: time-averaged O2 saturation values 30 minutes after dosing and the largest absolute fall in O2 saturation for each patient. RESULTS AND CONCLUSIONS: Time-averaged O2 saturation measures were higher in the proximal sideport group (p = 0.02), but the magnitude of difference was probably not clinically significant. No significant difference was detected between groups when we compared largest absolute drop in O2 saturation. Secondary analyses found no effect of birth weight or dose number (second vs third dose) on either outcome measure. 相似文献
2.
JD Nelson 《Canadian Metallurgical Quarterly》1996,335(12):885-886
3.
EH Eddes AM Masclee HG Gooszen M Fr?lich CB Lamers 《Canadian Metallurgical Quarterly》1997,174(4):387-392
Two mobilizable cloning vectors, designated pABW1 and pAWB2, were constructed basing on the E. coli vector pBGS18 and oriT originating from RK2. In pABW2 the kanamycin resistance gene was replaced by a novel tetracycline resistance cassette derived from Tn1721. Both vectors, specific for E. coli, allow to perform the cloning steps in E. coli and then to efficiently transfer the constructs by conjugation to the host of choice. A vector which cannot propagate in the given host can be applied for identification of the host specific plasmid replicator regions. With the use of pABW2 we defined the minimal replicator region of pTAV202-a mini-derivative of the large pTAV1 plasmid of P. versutus. We also proved that RepC' encoded on this fragment is the principal initiator replication protein and that oriV is located along its coding sequence. 相似文献
4.
In 1895 Trendelenburg described his sign to determine the integrity of hip function. We found the sign to be positive in a patient whose hip was clinically and radiologically normal, and therefore investigated this in other patients. We confirmed that a medial shift of the mechanical axis of the leg below the hip may cause a positive Trendelenburg sign. This has not been previously described. 相似文献
5.
A value-based test is presented for economic screening of electric utility demand-side management (DSM) programs. The widely used least cost test is valid if the programs do not alter the amount or value of energy services provided to customers. But, in general, DSM programs have such effects and, as a result, the value consumers receive is changed. A more general economic efficiency test, the most value test, provides a practical method for considering the effects of DSM on customer value. The version presented allows for multiple load periods and can account for rate impacts on several customer classes. Four typical DSM programs are evaluated as illustrations 相似文献
6.
7.
CB Verchere DA D'Alessio S Wang S Andrikopoulos SE Kahn 《Canadian Metallurgical Quarterly》1997,29(6):311-316
Islet amyloid polypeptide forms islet amyloid deposits in non-insulin-dependent diabetes mellitus. We have generated transgenic mice which express human islet amyloid polypeptide in their pancreatic beta cells yet do not develop islet amyloid deposits despite producing levels of the amyloidogenic human peptide 2 - 3 fold higher than the native (mouse) peptide. To determine whether marked overproduction of islet amyloid polypeptide is a potential cause of islet amyloid formation, we increased expression of this transgene by producing homozygous transgenic animals and by making heterozygous mice experimentally insulin resistant with nicotinic acid. Pancreatic content of islet amyloid polypeptide-like immunoreactivity in homozygous and nicotinic acid-treated mice was 2-fold (25 +/- 7 fmol/microg; n = 6) and 3.5-fold (47 +/- 20 fmol/microg; n = 3) higher, respectively, than that of untreated heterozygous animals (13+/-2 fmol/microg; n = 11; both p < 0.05). Despite this marked increase in production of islet amyloid polypeptide, neither group of mice developed gross islet amyloid deposits even after 16 months of age. We conclude that overproduction of islet amyloid polypeptide, even as produced by extreme insulin resistance, is not in itself sufficient for islet amyloid formation. 相似文献
8.
9.
Pentacene-based organic thin-film transistors 总被引:7,自引:0,他引:7
Yen-Yi Lin Gundlach D.I. Nelson S.F. Jackson T.N. 《Electron Devices, IEEE Transactions on》1997,44(8):1325-1331
Organic thin-film transistors using the fused-ring polycyclic aromatic hydrocarbon pentacene as the active electronic material have shown mobility as large as 0.7 cm2/V-s and on/off current ratio larger than 108; both values are comparable to hydrogenated amorphous silicon devices. On the other hand, these and most other organic TFT's have an undesirably large subthreshold slope. We show here that the large subthreshold slope typically observed is not an intrinsic property of the organic semiconducting material and that devices with subthreshold slope similar to amorphous silicon devices are possible 相似文献
10.
RM Bionta G Blewitt CB Bratton D Casper A Ciocio R Claus M Crouch ST Dye S Errede GW Foster W Gajewski KS Ganezer M Goldhaber TJ Haines TW Jones D Kielczewska WR Kropp JG Learned JM LoSecco J Matthews HS Park LR Price F Reines J Schulz S Seidel E Shumard D Sinclair HW Sobel JL Stone L Sulak R Svoboda G Thornton van der Velde JC C Wuest 《Canadian Metallurgical Quarterly》1987,36(1):30-36