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   23356篇
  免费   2176篇
  国内免费   13篇
  25545篇
  2023年   130篇
  2022年   337篇
  2021年   599篇
  2020年   280篇
  2019年   410篇
  2018年   465篇
  2017年   357篇
  2016年   628篇
  2015年   1096篇
  2014年   1148篇
  2013年   1511篇
  2012年   1777篇
  2011年   1754篇
  2010年   1090篇
  2009年   938篇
  2008年   1328篇
  2007年   1337篇
  2006年   1199篇
  2005年   1122篇
  2004年   1006篇
  2003年   953篇
  2002年   934篇
  2001年   306篇
  2000年   250篇
  1999年   237篇
  1998年   208篇
  1997年   162篇
  1996年   141篇
  1995年   128篇
  1994年   133篇
  1993年   146篇
  1992年   173篇
  1991年   155篇
  1990年   142篇
  1989年   139篇
  1988年   145篇
  1987年   118篇
  1986年   107篇
  1985年   124篇
  1984年   131篇
  1983年   90篇
  1982年   103篇
  1981年   89篇
  1979年   109篇
  1978年   85篇
  1977年   89篇
  1976年   81篇
  1975年   101篇
  1974年   83篇
  1973年   93篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
A variety of methylated 4-oxypiperidine derivatives were tested for their ability to inhibit protein synthesis in vitro. A direct correlation was found between the extent of methylation of these compounds and their inhibitory activity in a rabbit reticulocyte lysate cell-free translation system.Abbreviation IC50 50% inhibitory concentration  相似文献   
42.
43.
In a series of 68 patients with gastric ulcer who were treated by vagotomy and pyloroplasty there were no operative deaths, though one patient who received massive transfusions died 14 weeks later from hepatic necrosis probably associated with serum hepatitis. Four patients developed recurrent peptic ulceration requiring further surgical treatment. The clinical condition of all but three of the remainder was satisfactory after an average follow-up period of three years and two months. Of the 14 patients who presented with an acutely bleeding gastric ulcer, one subsequently required gastrectomy for continued bleeding; in all the others the immediate and long-term results were satisfactory. Of 21 patients with a “high” ulcer and 29 with combined gastric and duodenal ulceration one (4·8%) and three (10%) respectively suffered recurrences. We conclude that vagotomy and pyloroplasty is a satisfactory form of treatment for a high or bleeding gastric ulcer, but that for all other gastric ulcers some form of gastric resection is preferable.  相似文献   
44.
When pyrimidine deoxyribonucleosides are supplied to growing cultures of Diplococcus pneumoniae, they are selectively used for incorporation into deoxyribonucleic acid (DNA). Differently labeled molecules of deoxyuridine, thymidine, and deoxycytidine were used to study the precursor pathways of this organism. Each of these preformed pyrimidine deoxynucleosides is incorporated intact (i.e., without cleavage of the glycosidic bond) and is predominantly recoverable as DNA thymidine. During the utilization of deoxycytidine and deoxyuridine by pneumococci, large proportions of the available precursor are converted to free thymidine, which is secreted back into the growth medium. The biochemical pathways for selective incorporation into DNA and the regulation of concentrations of intracellular thymidine compounds by excretion of free thymidine are discussed.  相似文献   
45.
Dielectric dispersion measurements with aqueous solutions of hemoglobin and myoglobin have been performed in the frequency range from 100 kcps to 15 Mcps. The influence of preparation, particle size, and solvent conditions was studied. The results are analyzed in terms of an orientational polarization mechanism.  相似文献   
46.
Incomplete phagelike particles were found in competent and incompetent cells of Haemophilus influenzae Rd (transformable) lysed after exposure to ultraviolet radiation.  相似文献   
47.
Ninety patients who had a recurrence of thyrotoxicosis after thyroidectomy have been reviewed. All 10 patients who had a second operation and 18 out of 20 patients treated with a full course of antithyroid drugs relapsed. These results differ greatly from the results of treatment of the first episode of thyrotoxicosis, whether by thyroidectomy or antithyroid drugs. Radioiodine is the treatment of choice in this group of patients, despite the high incidence of hypothyroidism.  相似文献   
48.
49.
A rapid test for the recognition of aflatoxin-synthesizing strains of the Aspergillus flavus–oryzae group is described. For this purpose the strains are cultivated on Czapek–Dox agar enriched with an aqueous extract of groundnuts, and in which sodium nitrate is replaced by ammonium chloride. Toxin production is observed by the production of a bright blue fluorescence in the medium when placed under an ultraviolet lamp.  相似文献   
50.
Xp-duplications with and without sex reversal   总被引:5,自引:0,他引:5  
Duplications in Xp including the DSS (dosage sensitive sex reversal) region cause male to female sex reversal. We investigated two patients from families with Xp duplications. The first case was one of two sisters with karyotype 46,XY, der(22), t(X;22)(p11.3;p11)mat and unambiguous female genitalia. The living sister was developmentally retarded, and showed multiple dysmorphic features and an acrocallosal syndrome. The second case was a boy with a maternally inherited direct duplication of Xp21.3-pter with the breakpoint close to the DSS locus. He had multiple abnormalities and micropenis, but otherwise unambiguous male genitalia. We performed quantitative Southern blot analysis with probes from Xp22.13 to p21.2 to define the duplicated region. Clinical, cytogenetic, and molecular data from both patients were compared with those of previously reported related cases. A comparison of the extragenital symptoms revealed no differences between patients with or without sex reversal. In both cases, the symptoms were non-specific. Among 22 patients with a duplication in Xp, nine had unambiguous female genitalia and a well-documented duplication of the DSS region. Two patients with duplication of DSS showed ambiguous external genitalia. From these data, we conclude that induction of testicular tissue may start in these patients, but that the type of genitalia depends on the degree of subsequent degeneration by a gene in DSS.  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