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   3285篇
  免费   199篇
  2023年   5篇
  2022年   16篇
  2021年   34篇
  2020年   20篇
  2019年   37篇
  2018年   52篇
  2017年   55篇
  2016年   79篇
  2015年   112篇
  2014年   144篇
  2013年   181篇
  2012年   220篇
  2011年   217篇
  2010年   155篇
  2009年   160篇
  2008年   251篇
  2007年   222篇
  2006年   231篇
  2005年   224篇
  2004年   231篇
  2003年   169篇
  2002年   204篇
  2001年   32篇
  2000年   32篇
  1999年   35篇
  1998年   37篇
  1997年   29篇
  1996年   34篇
  1995年   19篇
  1994年   25篇
  1993年   19篇
  1992年   17篇
  1991年   18篇
  1990年   21篇
  1989年   15篇
  1988年   9篇
  1987年   12篇
  1986年   12篇
  1985年   16篇
  1984年   16篇
  1983年   17篇
  1982年   8篇
  1981年   4篇
  1980年   3篇
  1979年   7篇
  1978年   3篇
  1977年   4篇
  1975年   4篇
  1974年   3篇
  1970年   3篇
排序方式: 共有3484条查询结果,搜索用时 31 毫秒
31.
32.
Summary Fine structural features of pinealocytes of cotton rats (Sigmodon hispidus) were examined. Golgi complexes, mitochondria, endoplasmic reticulum and polysomes are usual organelles seen in the perikaryonal cytoplasm of pinealocytes. Many non-granulated vesicles (40 to 80 nm in diameter) and a few granulated vesicles (about 100 nm in diameter) are associated with the Golgi cisternae. Occasionally, the cisternae contain granular materials. The perikaryonal cytoplasm of pinealocytes is characterized by the presence of inclusion bodies. These bodies are usually round in shape, not bounded by a limiting membrane and composed of fine granular or filamentous materials of high electron-opacity, which are similar in appearance to the substance seen in the nucleolonema. Pinealocyte processes, filled with abundant non-granulated vesicles and some granulated vesicles, are mainly found within the parenchyma and occasionally in perivascular spaces.Supported in part by NSF grant no. PCM 77-05734 and NIH grant no. HD-10202 (Morphology Core)  相似文献   
33.
An effective and economical method was developed for procuring and rearing calves in gnotobiotic conditions. To evaluate apparatuses and surgical techniques, three calves, 1 to 3, welf 1 was weak and pale at delivery and died within 5 hours after delivery. Calf 2 was delivered alive, but died from a human error at 3 days of age. It was free from demonstrable bacteria and fungi at that time. Calf 3 was also successfully delivered and raised. It was killed at 10 days of age, since fungi were isolated from the feces and waste materials from it.  相似文献   
34.
We attempted to optimize sulfonamide-based non-alkyne LpxC inhibitors by focusing on improvements in enzyme inhibitory and antibacterial activity. It was discovered that inhibitors possessing 2-aryl benzofuran as a hydrophobe exhibited good activity. In particular, compound 21 displayed impressive antibacterial activity (E. coli MIC = 0.063 μg/mL, K. pneumoniae MIC = 0.5 μg/mL, and P. aeruginosa MIC = 0.5 μg/mL), and is a promising lead for further exploration as an antibacterial agent.  相似文献   
35.
The effects of nucleoid proteins Fis and Dps of Escherichia coli on the higher order structure of a giant DNA were studied, in which Fis and Dps are known to be expressed mainly in the exponential growth phase and stationary phase, respectively. Fis causes loose shrinking of the higher order structure of a genome-sized DNA, T4 DNA (166 kbp), in a cooperative manner, that is, the DNA conformational transition proceeds through the appearance of a bimodal size distribution or the coexistence of elongated coil and shrunken globular states. The effective volume of the loosely shrunken state induced by Fis is 30–60 times larger than that of the compact state induced by spermidine, suggesting that cellular enzymes can access for DNA with the shrunken state but cannot for the compact state. Interestingly, Dps tends to inhibit the Fis-induced shrinkage of DNA, but promotes DNA compaction in the presence of spermidine. These characteristic effects of nucleotide proteins on a giant DNA are discussed by adopting a simple theoretical model with a mean-field approximation.  相似文献   
36.
37.
It has been reported that c-erb A encodes nuclear T3 receptors (NT3R). Based on the sequence of c-erb A cDNA, we synthesized a polypeptide consisting of 15 amino acids, the sequence of which has high homology between c-erb A alpha 1 and beta. The antibody against this c-erb A peptide not only immunoprecipitated rat liver and kidney NT3R but also inhibited T3 binding to NT3R. In a displacement study, the inhibition of [125I]T3-binding by the antibody was parallel to that by T3 in terms of the concentration of the competitor added in the incubation mixture. Scatchard analysis revealed that the antibody decreased the value for the association constant in a dose dependent manner. The antibody did not bind T3 itself. The results show that the antibody against c-erb A peptide recognizes rat liver and kidney NT3R and that the sequence encoding this peptide, the closest carboxyl-terminal of c-erb A may be critical or at least closely related to the hormone binding.  相似文献   
38.
Post‐inflammatory hyperpigmentation (PIH) is a common cutaneous condition that can cause a disfigured appearance. However, the pathophysiology of PIH remains poorly understood, at least in part, because an appropriate animal model for research has not been established. In order to analyze the pathomechanism of PIH, we successfully induced PIH in a hairless version of transgenic mice (hk14‐SCF Tg/HRM) that have a human‐type epidermis containing melanin by repeated hapten application of 2,4‐dinitrofluorobenzene. Histopathologic observation showed epidermal hyperplasia, predominant infiltrations of inflammatory cells, and melanin‐containing cells in the dermis just after elicitation of the atopic dermatitis‐like condition. At week 2, the findings were similar to the characteristics of PIH, that is, an increase of melanin without spongiosis or liquid degeneration in the epidermis and an increase in dermal melanophages. Dynamic analysis of melanin showed that the melanin in the dermis remained for a longer duration than in the epidermis. Furthermore, immunohistochemical staining revealed that the majority of cells containing melanin were positive for the anti‐CD68 antibody, but negative for the anti‐F4/80 antibody. These data suggest that novel treatments of PIH should be targeted against macrophages and should eventually lead to the development of new treatment modalities.  相似文献   
39.
Abstract

This paper presents a boosting effect against gravity by analyzing the displacement and stress distribution of craniofacial structures due to the protraction of the extraoral device, the Right Angle Maxillary Protraction Appliance(RAMPA) system, including semi-rapid maxillary expansion (sRME) using the finite element method. In addition, a patient case was illustrated and compared with the results calculated from a simulation. The results from the finite element method were obtained for 0.5?mm activation using the screw of the intraoral device, gHu-1. This study reveals that RAMPA rotates the patient’s maxilla and mandible in the forward direction and forces them to move forward and upward.  相似文献   
40.
The chemical properties of Amadori compounds in the presence of transition metal ions were studied, using the analogs 1-deoxy-1- n -butylamino- d -fructose (DBF) and N &#102 -formyl-fructoselysine (fFL). The following characteristics were revealed: (a) DBF combined easily with Cu 2+ (but no other transition metal ions) to form a DBF-Cu 2+ complex in phosphate buffer, pH 7.4; (b) the complex was unstable, and degraded with the release of Cu + during incubation at 37°C; (c) degradation of the complex was associated with the production of hydroxyl radicals by the Fenton reaction and &#102 -dicarbonyl compounds by non-autoxidative degradation; and (d) properties of DBF were similar to those of fFL. The above properties were additionally observed in glycated poly-Lys (GPL). Our findings indicate a novel mechanism for the generation of hydroxyl radicals and &#102 -dicarbonyl compounds from Amadori adducts in the presence of Cu 2+ .  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