首页 | 本学科首页   官方微博 | 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   138484篇
  免费   4250篇
  国内免费   814篇
  2023年   226篇
  2021年   384篇
  2020年   321篇
  2019年   344篇
  2018年   12583篇
  2017年   11407篇
  2016年   8333篇
  2015年   1537篇
  2014年   1432篇
  2013年   2303篇
  2012年   7411篇
  2011年   16148篇
  2010年   13572篇
  2009年   9311篇
  2008年   12525篇
  2007年   14084篇
  2006年   3170篇
  2005年   3116篇
  2004年   3432篇
  2003年   3285篇
  2002年   3058篇
  2001年   1769篇
  2000年   1906篇
  1999年   958篇
  1998年   496篇
  1997年   395篇
  1996年   442篇
  1995年   381篇
  1994年   412篇
  1993年   402篇
  1992年   404篇
  1991年   357篇
  1990年   315篇
  1989年   277篇
  1988年   277篇
  1987年   269篇
  1986年   219篇
  1985年   318篇
  1984年   388篇
  1983年   353篇
  1982年   317篇
  1981年   303篇
  1980年   271篇
  1979年   261篇
  1978年   269篇
  1977年   242篇
  1976年   248篇
  1975年   291篇
  1972年   375篇
  1971年   421篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.

Background  

Recent studies point to a great diversity of non-ribosomal peptide synthesis systems with major roles in amino acid and co-factor biosynthesis, secondary metabolism, and post-translational modifications of proteins by peptide tags. The least studied of these systems are those utilizing tRNAs or aminoacyl-tRNA synthetases (AAtRS) in non-ribosomal peptide ligation.  相似文献   
12.
13.
A critical factor in clinical development of cancer immunotherapies is the identification of tumor-associated antigens that may be related to immunotherapy potency. In this study, protein microarrays containing >8,000 human proteins were screened with serum from prostate cancer patients (N = 13) before and after treatment with a granulocyte–macrophage colony-stimulating factor (GM-CSF)-secreting whole cell immunotherapy. Thirty-three proteins were identified that displayed significantly elevated (P ≤ 0.05) signals in post-treatment samples, including three proteins that have previously been associated with prostate carcinogenesis, galectin-8, T-cell alternative reading frame protein (TARP) and TNF-receptor-associated protein 1 (TRAP1). Expanded analysis of antibody induction in metastatic, castration-resistant prostate cancer (mCRPC) patients (N = 92) from two phase 1/2 trials of prostate cancer immunotherapy, G-9803 and G-0010, indicated a significant (P = 0.03) association of TARP antibody induction and median survival time (MST). Antibody induction to TARP was also significantly correlated (P = 0.036) with an increase in prostate-specific antigen doubling time (PSADT) in patients with a biochemical (PSA) recurrence following prostatectomy or radiation therapy (N = 19) from in a previous phase 1/2 trial of prostate cancer immunotherapy, G-9802. RNA and protein encoding TARP and TRAP1 was up-regulated in prostate cancer tissue compared to matched normal controls. These preliminary findings suggest that antibody induction to TARP may represent a possible biomarker for treatment response to GM-CSF secreting cellular immunotherapy in prostate cancer patients and demonstrates the utility of using protein microarrays for the high-throughput screening of patient-derived antibody responses.  相似文献   
14.
15.

Background  

Substituted catechols are important precursors for large-scale synthesis of pharmaceuticals and other industrial products. Most of the reported chemical synthesis methods are expensive and insufficient at industrial level. However, biological processes for production of substituted catechols could be highly selective and suitable for industrial purposes.  相似文献   
16.
In a section of the Liassic southwest of the village of Préjano (Prov. Logroño) Sinemurian Dasyclad algae were found for the first time in the “Bankkalk-Series” of the “Carniolas-Formation” which is not dated up to that time. Six species,Dissocladella lucasi (Cros & Lemoine),Dissocladella iberica nov. sp.,Dissocladella ebroensis nov. sp.,Sestrosphaera liasina Pia,Gyroporella retica (Zanin) andMacroporella nov. sp. aff. sturi Bystricky are described.  相似文献   
17.
18.
19.
Georg Söderbom 《Ethnos》2013,78(1-2):95-100
Current debates over the concept of culture are examined, especially with regard to the relationship of culture to bounded collectivities, human nature, and individuality; present‐day views are seen against the background of back‐and‐forth swings in the history of anthropological thought. Recent theorizing about cultural acquisition is also considered.  相似文献   
20.
Food availability is important to the dynamics of animal social organizations or populations. However, the role of winter food availability in animal population dynamics is still controversial. We carried out an experimental study to test Lack’s hypothesis that reduced food in winter limits survival and spring numbers of breeding individuals of social groups, using the Mongolian gerbil (Meriones unguiculatus) as model species. We established 24 gerbil social groups in 24, 10 × 10 m, pens in September 2008. We provided wheat seeds as supplemental food in 12 enclosures from September 2008 to March 2009; the other 12 enclosures, not provided with supplemental food, served as controls. We live-trapped gerbils at a 2-week interval from September to April. Supplemental food during winter increased biweekly survival by 10% relative to that in control groups. Only four control social groups survived to the end of our study whereas all 12 food-supplemented social groups survived through our study period. Supplemental food also increased cumulative numbers of recruits and group sizes of gerbils. We conclude that winter food availability limits winter survival and spring social groups or population sizes of Mongolian gerbils.  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