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   6321篇
  免费   327篇
  国内免费   3篇
  2022年   19篇
  2021年   57篇
  2020年   32篇
  2019年   70篇
  2018年   98篇
  2017年   58篇
  2016年   114篇
  2015年   165篇
  2014年   221篇
  2013年   406篇
  2012年   393篇
  2011年   348篇
  2010年   241篇
  2009年   231篇
  2008年   382篇
  2007年   381篇
  2006年   371篇
  2005年   356篇
  2004年   379篇
  2003年   366篇
  2002年   361篇
  2001年   129篇
  2000年   133篇
  1999年   117篇
  1998年   83篇
  1997年   65篇
  1996年   62篇
  1995年   52篇
  1994年   56篇
  1993年   52篇
  1992年   104篇
  1991年   58篇
  1990年   70篇
  1989年   68篇
  1988年   77篇
  1987年   38篇
  1986年   46篇
  1985年   34篇
  1984年   31篇
  1983年   40篇
  1982年   38篇
  1981年   29篇
  1980年   24篇
  1979年   24篇
  1978年   16篇
  1977年   17篇
  1976年   13篇
  1975年   24篇
  1974年   17篇
  1973年   24篇
排序方式: 共有6651条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
5.
6.
Several modification of the arrangements of α-helical molecules were found in the solid films of poly (γ-ethyl-L -glutamate), depending on the casting solvent and the temperature. The helical conformation is somewhat looser than the normal 18-residue, 5-turn α-helix. Using x-ray diffraction, the types of molecular arrangements were classified into tetragonal, pseudohexagonal, and hexagonal ones. Tetragonal packing was observed in the filmm (form T) prepared by casting the solution in trifluorethanol or dichlorethane. The sample obtained from chloroform solution is a well-ordered, pseudohexagonal modification (form I). Forms I and T change into a poorly crystalline form III by annealing at temperatures above 130° C. It is particularly noteworthy that the less-ordered form III exhibits a thermoreversible transition around 110°C into a well-ordered form H with the hexagonal molecular packing.  相似文献   
7.
8.
9.
Defective interfering (DI) influenza viruses carry a large deletion in a gene segment that interferes with the replication of infectious virus; thus, such viruses have potential for antiviral therapy. However, because DI viruses cannot replicate autonomously without the aid of an infectious helper virus, clonal DI virus stocks that are not contaminated with helper virus have not yet been generated. To overcome this problem, we used reverse genetics to generate a clonal DI virus with a PB2 DI gene, amplified the clonal DI virus using a cell line stably expressing the PB2 protein, and confirmed its ability to interfere with infectious virus replication in vitro. Thus, our approach is suitable for obtaining purely clonal DI viruses, will contribute to the understanding of DI virus interference mechanisms and can be used to develop DI virus‐based antivirals.  相似文献   
10.
Moyamoya disease (MMD) is a chronic, progressive, cerebrovascular occlusive disease that causes abnormal enlargement of collateral pathways (moyamoya vessels) in the region of the basal ganglia and thalamus. Cerebral revascularization procedures remain the preferred treatment for patients with MMD, improving the compromised cerebral blood flow (CBF). However, voxel based analysis (VBA) of revascularization surgery for MMD based on data from pre- and postoperative data has not been established. The latest algorithm called as Diffeomorphic Anatomical Registration Through Exponentiated Lie Algebra (DARTEL) has been introduced for VBA as the function of statistical parametric mapping (SPM8), and improved registration has been achieved by SPM8 with DARTEL. In this study, VBA was conducted to evaluate pre- and postoperative single photon emission computed tomography (SPECT) images for MMD by SPM8 with DARTEL algorithm, and the results were compared with those from SPM8 without DARTEL (a conventional method). Thirty-two patients with MMD who underwent superficial temporal artery-middle cerebral artery (STA-MCA) bypass surgery as the first surgery were included and all patients underwent pre- and postoperative 3D T1-weighted imaging and SPECT. Pre- and postoperative SPECT images were registered to 3D T1-weighted images, then VBA was conducted. Postoperative SPECT showed more statistically increased CBF areas in the bypassed side cerebral hemisphere by using SPM8 with DARTEL (58,989 voxels; P<0.001), and increased ratio of CBF after operation was less than 15%. Meanwhile, postoperative SPECT showed less CBF increased areas by SPM8 without DARTEL. In conclusion, VBA was conducted for patients with MMD, and SPM8 with DARTEL revealed that postoperative SPECT showed statistically significant CBF increases over a relatively large area and with at most 15% increase ratio.  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