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   5471篇
  免费   525篇
  国内免费   100篇
工业技术   6096篇
  2024年   14篇
  2023年   131篇
  2022年   167篇
  2021年   344篇
  2020年   222篇
  2019年   210篇
  2018年   254篇
  2017年   237篇
  2016年   228篇
  2015年   192篇
  2014年   224篇
  2013年   351篇
  2012年   271篇
  2011年   304篇
  2010年   252篇
  2009年   231篇
  2008年   247篇
  2007年   215篇
  2006年   196篇
  2005年   155篇
  2004年   153篇
  2003年   118篇
  2002年   143篇
  2001年   62篇
  2000年   69篇
  1999年   66篇
  1998年   142篇
  1997年   98篇
  1996年   76篇
  1995年   69篇
  1994年   57篇
  1993年   50篇
  1992年   45篇
  1991年   36篇
  1990年   36篇
  1989年   41篇
  1988年   19篇
  1987年   35篇
  1986年   26篇
  1985年   41篇
  1984年   39篇
  1983年   23篇
  1982年   22篇
  1981年   18篇
  1980年   23篇
  1979年   19篇
  1977年   16篇
  1976年   22篇
  1974年   13篇
  1973年   12篇
排序方式: 共有6096条查询结果,搜索用时 312 毫秒
51.
A B16 melanoma-specific CD8+ T cell line (AB1) was established from the spleen cells of C57BL/6 mice cured of B16 melanoma with interleukin (IL)-12 treatment. The AB1 line exclusively used T cell receptor Vbeta11. The AB1 cells exhibited a cytolytic activity against both syngeneic B16 melanoma and allogeneic P815 mastocytoma, whereas a cold inhibition assay revealed specificity of the AB1 cells against B16 melanoma. Their lostability to kill a class I loss variant of B16 melanoma was restored by the transfection of H-2Kb gene. In addition, their interferon (IFN)-gamma production was significantly suppressed by the addition of anti-H-2Kb monoclonal antibody, and RT-PCR analysis showed that the AB1 line expressed the mRNA encoding IFN-gamma, but not IL-4 or IL-10. The experiment using synthetic peptides of tyrosinase-related protein-2 (TRP-2) revealed that the AB1 cells could recognize TRP-2(181-188) peptide. Moreover, the AB1 cells showed an in vivo antitumor effect against established pulmonary metastases of B16 melanoma. Overall, these results indicate that the Tc1-type Vbeta11+ AB1 cells exert an antitumor activity against syngeneic B16 melanoma through recognition of TRP-2(181-188) peptide in an H-2Kb-restricted manner.  相似文献   
52.
We analysed 42 differentiated thyroid tumors including 15 follicular adenomas (FA), 13 papillary thyroid cancers (PTC) and 14 follicular thyroid carcinomas (FTC) with 13 microsatellite markers specific for the long arm of human chromosome 7 within 7q31; this region is deleted frequently in several other tumor types. Overall, 20 of the 42 samples analysed (48%) displayed LOH with one or more of the markers tested. LOH was detected most frequently (78%) in FTC, the most malignant of the thyroid tumors. A smallest common deleted region (SCDR) was defined in this tumor type flanked by markers D7S480 and D7S490. This SCDR is distinct from D7S522, the most commonly deleted locus in many other tumors, which was deleted in only one FTC. D7S522 did show LOH in two of six informative PTCs. None of the PTC and only two of the FAs showed LOH in the FTC SCDR. Since FA is considered a premalignant stage of FTC, our results suggest that inactivation of a putative tumor suppressor at 7q31.2 may be acquired during adenoma to carcinoma progression. The absence of LOH at this locus amongst PTC suggests that inactivation of this tumor suppressor is specific for FTC. In conclusion, LOH at 7q31 is a frequent event in differentiated thyroid cancer, and we have defined a 2 cM SCDR specific for FTC.  相似文献   
53.
Since Samuel's work on checkers over thirty years ago, much effort has been devoted to learning evaluation functions. However, all such methods are sensitive to the feature set chosen to represent the examples. If the features do not capture aspects of the examples significant for problem solving, the learned evaluation function may be inaccurate or inconsistent. Typically, good feature sets are carefully handcrafted and a great deal of time and effort goes into refining and tuning them. This paper presents an automatic knowledge-based method for generating features for evaluation functions. The feature set is developed iteratively: features are generated, then evaluated, and this information is used to develop new features in turn. Both the contribution of a feature and its computational expense are considered in determining whether and how to develop it further.
This method has been applied to two problem-solving domains: the Othello board game and the domain of telecommunications network management. Empirical results show that the method is able to generate many known features and several novel features and to improve concept accuracy in both domains.  相似文献   
54.
The present study has examined the distribution of axons of differing sizes in the optic pathway of the ground squirrel. Axon diameters were measured from electron micrographs at various locations across sections of the optic nerve and tract, and total distributions and numbers were estimated. In both the nerve and tract, roughly 1.2 million optic axons were present. The population of optic axons had a unimodal size distribution, peaking at 0.9 microm in diameter and having an extended tail toward larger diameters. Local axon diameter distributions in the optic tract indicated distinct (though partially overlapping) axon diameter classes, including one of fine sizes peaking at 0.8-0.9 microm, a second of medium sizes peaking around 1.7-1.8 microm, and a third composed of the larger fibers with diameters up to 4.8 microm. The fine-caliber axons were found at all locations in the tract, and were the only axons present immediately adjacent to the pia, while the medium- and coarse-caliber axons were found at deeper locations. Curiously, the larger axons were found primarily in the medial parts of the tract, where axons from the dorsal retina normally course. A similarly restricted distribution of the larger axons was observed in the dorsotemporal parts of the optic nerve, suggesting that this difference in the tract may relate to an asymmetric distribution of ganglion cells on the retina giving rise to these axons. Measurements of axonal size taken within the optic fiber layer in dorsal and ventral parts of the retina confirmed this asymmetry, consistent with previous demonstrations of soma size differences in the dorsal versus ventral retina. The partial segregation of axons by size in the optic tract of the ground squirrel then reflects both the asymmetric distribution of retinal ganglion cell classes and the chronotopic reordering of optic axons that occurs within the chiasmatic region.  相似文献   
55.
The Women's Health Trial:Feasibility Study in Minority Populations (WHT:FSMP) examined the feasibility of recruiting postmenopausal women from a broad range of racial and socioeconomic backgrounds into a primary prevention trial requiring marked reductions in dietary fat. Postmenopausal women aged 50-79 yr who had no history of cardiovascular disease or cancer and who consumed 36% or more total energy from fat qualified to participate. We randomized the women into dietary intervention (60%) or control (40%) groups; we aimed to randomize 750 women in 18 months in each of the three clinical centers. All centers achieved goals for randomization based on ethnicity, and two centers exceeded overall recruitment goals. The greatest source of randomized participants was mass mailing, followed by items in the media, referrals, and community outreach. Recruitment yields were generally similar for the ethnic groups but lower for less-educated participants. The experience of WHT:FSMP indicates that postmenopausal women from the African-American, Hispanic, and non-Hispanic white communities can be recruited into dietary intervention studies for the prevention of disease.  相似文献   
56.
57.
Sun  Zhandong  Lotz  Tom  Huang  Qun 《Water Resources Management》2021,35(3):1065-1077
Water Resources Management - Parameter calibration is a core process for the application of distributed hydrological models, which depends strongly on river runoff records. However, the sparse...  相似文献   
58.
Water Resources Management - Sustained pumping of groundwater can lead to declining water levels in wellfields and concerns regarding the sustainability of groundwater resources. Aquifer Storage...  相似文献   
59.
以渭河拦河闸为例,基于ADINA有限元分析软件,建立拦河闸三维有限元模型,采用振型分解反应谱法对闸室结构进行地震动响应计算分析,并根据计算结果对拦河闸进行抗震安全评价。计算结果表明:拦河闸闸室结构前5阶振型主要体现为横梁和机架桥结构的振动,符合一般规律;边孔横梁与机架桥联接部位以及机架桥与闸墩联接部位出现了较大拉应力,其最大拉应力数值超过了混凝土动态抗拉强度标准值,但考虑局部配筋量后,拉应力数值满足安全需求;在地震作用最不利工况下,拦河闸整体闸室结构抗滑稳定安全因数为1.68,满足安全需求;拦河闸抗震安全满足标准要求,其抗震等级评定为A级。  相似文献   
60.
The Internet of Things (IoT) concept is being widely presented as the next revolution toward massively distributed information, where any real-world object can automatically participate in the Internet and thus be globally discovered and queried. Despite the consensus on the great potential of the concept and the significant progress in a number of enabling technologies, there is a general lack of an integrated vision on how to realize it. This paper examines the technologies that will be fundamental for realizing the IoT and proposes an architecture that integrates them into a single platform. The architecture introduces the use of the Smart Object framework to encapsulate radio-frequency identification (RFID), sensor technologies, embedded object logic, object ad-hoc networking, and Internet-based information infrastructure. We evaluate the architecture against a number of energy-based performance measures, and also show that it outperforms existing industry standards in metrics such as network throughput, delivery ratio, or routing distance. Finally, we demonstrate the feasibility and flexibility of the architecture by detailing an implementation using Wireless Sensor Networks and Web Services, and describe a prototype for the real-time monitoring of goods flowing through a supply chain.  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