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   2835篇
  免费   209篇
  国内免费   11篇
耳鼻咽喉   21篇
儿科学   104篇
妇产科学   112篇
基础医学   416篇
口腔科学   131篇
临床医学   348篇
内科学   564篇
皮肤病学   118篇
神经病学   153篇
特种医学   42篇
外科学   189篇
综合类   52篇
一般理论   5篇
预防医学   249篇
眼科学   71篇
药学   232篇
中国医学   55篇
肿瘤学   193篇
  2024年   8篇
  2023年   54篇
  2022年   169篇
  2021年   225篇
  2020年   166篇
  2019年   192篇
  2018年   195篇
  2017年   109篇
  2016年   146篇
  2015年   119篇
  2014年   167篇
  2013年   196篇
  2012年   258篇
  2011年   240篇
  2010年   120篇
  2009年   86篇
  2008年   121篇
  2007年   105篇
  2006年   88篇
  2005年   97篇
  2004年   67篇
  2003年   32篇
  2002年   33篇
  2001年   5篇
  2000年   2篇
  1999年   7篇
  1998年   2篇
  1997年   3篇
  1996年   3篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1991年   1篇
  1990年   1篇
  1988年   5篇
  1987年   7篇
  1986年   2篇
  1985年   5篇
  1984年   2篇
  1980年   1篇
  1979年   4篇
  1977年   1篇
  1976年   1篇
  1973年   2篇
  1936年   1篇
排序方式: 共有3055条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
46.
In this paper, an efficient and straightforward synthetic approach for the preparation of a number of symmetric carboxylic anhydrides was reported using Cu2(BDC)2(DABCO) as an efficient heterogeneous catalyst via the C–H bond activation of aldehydes with excellent yields and simple work up. This C–H bond activation reaction appears simple and convenient, has a wide substrate scope and makes use of cheap, abundant, and easily available reagents. The Cu-MOF catalyst was recycled and reused four times without any loss of catalytic activity.

In this paper, an efficient synthetic method for the preparation of symmetric carboxylic anhydrides was reported using Cu2(BDC)2(DABCO) as an efficient heterogeneous catalyst via the C–H bond activation of aldehydes with good yields and simple work up.  相似文献   
47.

Background:

Haemonchosis has a negative effect on the farming industry throughout the world, especially in the tropic and sub-tropic countries. The present study was carried out to differentiate Haemonchus species from its main hosts in Iran, including sheep, goat and camel.

Methods:

The identification took place based on the morphometrics of the spicules and molecular characters. Two hundred seventy adult male nematodes were collected from the abomasums of different ruminants (90 samples from each animal) at the slaughterhouses from different localities in Iran. Samples were morphologically identified according to the spicules’ morphometric measurements. In the section on molecular study, 10 samples of each Haemonchus isolates were genetically examined. A simple PCR-restriction fragment length polymorphism (PCR-RFLP) assay of the second internal transcribed spacer of ribosomal DNA (ITS2-rDNA) were described to confirm the PCR results.

Results:

PCR-RFLP profile obtained from the restriction enzyme HPa1 in H. contortus and H. longistipes indicated 1 (278 bp) and 2 (113 and 135 bp) different fragments, respectively. The morphological parameters clearly distinguish H. contortus from H. longistipes. Moreover, regarding the ITS2-rDNA, sequences of 295 bp and 314 bp were obtained from H. contortus and H. longistipes, respectively.

Conclusion:

The genotypic results are in agreement with the phenotypic findings of both species.  相似文献   
48.
Phosphorus-containing compounds are one of the most important classes of organic compounds, which have wide applications in organic chemistry, medicinal chemistry, agricultural chemistry, and materials chemistry. In particular, organophosphorus compounds bearing a P(O)–C bond have attracted significant attention in recent decades due to their widespread biological and pharmacological activities. In this review, we will highlight the most important developments in the construction of P(O)–C bonds through decarboxylative C–P cross-coupling reactions. The literature has been surveyed from 2011 to May 2018.

Phosphorus-containing compounds are one of the most important classes of organic compounds, which have wide applications in organic chemistry, medicinal chemistry, agricultural chemistry, and materials chemistry.  相似文献   
49.
Clinical Rheumatology - Considering the pathologic significance of inflammation and oxidative stress in rheumatoid arthritis (RA) as well as the antioxidant, anti-inflammatory and hypolipidemic...  相似文献   
50.
Clinical Rheumatology - The clinical benefits of rituximab in systemic sclerosis (SSc) are still contentious. The present meta-analysis aimed to systematically assess rituximab’s safety and...  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