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   2308篇
  免费   225篇
  国内免费   1篇
  2023年   9篇
  2022年   35篇
  2021年   75篇
  2020年   42篇
  2019年   39篇
  2018年   43篇
  2017年   52篇
  2016年   67篇
  2015年   110篇
  2014年   127篇
  2013年   134篇
  2012年   164篇
  2011年   158篇
  2010年   99篇
  2009年   87篇
  2008年   104篇
  2007年   88篇
  2006年   79篇
  2005年   72篇
  2004年   77篇
  2003年   84篇
  2002年   63篇
  2001年   55篇
  2000年   60篇
  1999年   50篇
  1998年   23篇
  1997年   18篇
  1996年   12篇
  1995年   29篇
  1994年   23篇
  1993年   25篇
  1992年   39篇
  1991年   30篇
  1990年   34篇
  1989年   26篇
  1988年   36篇
  1987年   29篇
  1986年   23篇
  1985年   31篇
  1984年   18篇
  1983年   16篇
  1982年   11篇
  1979年   17篇
  1978年   10篇
  1975年   8篇
  1974年   11篇
  1973年   14篇
  1972年   11篇
  1969年   7篇
  1967年   7篇
排序方式: 共有2534条查询结果,搜索用时 31 毫秒
51.
Simian retroperitoneal fibromatosis (RF) is a vascular fibroproliferative neoplasm which has many morphological and histological similarities to human Kaposi's sarcoma (KS). Like epidemic KS in AIDS patients, RF is highly associated with an immunodeficiency syndrome (simian acquired immunodeficiency syndrome [SAIDS]) caused by a retrovirus infection. Recently, a new gammaherpesvirus, called Kaposi's sarcoma-associated herpesvirus (KSHV) or human herpesvirus 8 (HHV8), has been identified in KS tumors, suggesting that KS has a viral etiology. Our previous experimental transmission studies and epidemiological data suggest that RF also has an infectious etiology. In order to determine whether a similar virus is also associated with RF, we have assayed for the presence of an unknown herpesvirus using degenerate PCR primers targeting the highly conserved DNA polymerase genes of the herpesvirus family. Here we provide DNA sequence evidence for two new herpesviruses closely related to KSHV from RF tissues of two macaque species, Macaca nemestrina and Macaca mulatta. Our data suggest that KSHV and the putative macaque herpesviruses define a new group within the subfamily Gammaherpesvirinae whose members are implicated in the pathogenesis of KS and KS-like neoplasms in different primate species.  相似文献   
52.
Peptide VP1 (11-25) of the capsid of hepatitis A virus was synthesized by the Fmoc-polyamide solid phase method, and administered to mice in different forms: (1) free, (2) encapsulated in multilamellar liposomes, (3) coupled to keyhole limpet hemocyanin (KHL), and (4) incorporated into a tetrameric branched lysine core. The highest anti-VP1 peptide responses were generated by synthetic peptides entrapped into liposomes and coupled to KLH. No anti-HAV response was generated with the free peptide, while all the other forms induced both anti-HAV and HAV-neutralizing antibodies. Maximum neutralization indices were observed in ascites from mice treated with liposome-entrapped and KLH peptides.  相似文献   
53.
Five clones, containing polymorphic CA-repeat sequences, have been isolated from a specific human chromosome 21 phage library and have been localised to band q21 of chromosome 21 using a somatic cell hybrid panel. These highly repetitive sequences (D21S1263, D21S1264, D21S1415, D21S1417 and D21S1420) have been characterised in the CEPH reference parents and have heterozygosities ranging from 0.30 to 0.81 and an average polymorphism information content (PIC) of 0.62. The relative order of these markers, based on the somatic cell hybrid panel, is cen-D21S1417, D21S1420-D21S1263, D21S1415-D21S1264-tel. The most polymorphic marker (D21S1264) has been included in the chromosome 21 genetic map. They have also been localised in the CEPH/ Généthon YAC panel, providing a refined localisation of these polymorphic sequences. These five CA-repeat markers should provide a better characterisation of the q21 region of chromosome 21.  相似文献   
54.
Advertisement calls of Bolivian Leptodactylidae (Amphibia, Anura)   总被引:1,自引:0,他引:1  
R. Marquez    I. de la  Riva  J. Bosch 《Journal of Zoology》1995,237(2):313-336
  相似文献   
55.
Type strains of 200 species of yeasts able to ferment glucose and grow on xylose were screened for fermentation of d-xylose. In most of the strains tested, ethanol production was negligible. Nineteen were found to produce between 0.1 and 1.0 g of ethanol per liter. Strains of the following species produce more than 1 g of ethanol per liter in the fermentation test with 2% xylose: Brettanomyces naardenensis, Candida shehatae, Candida tenuis, Pachysolen tannophilus, Pichia segobiensis, and Pichia stipitis. Subsequent screening of these yeasts for their capacity to ferment d-cellobiose revealed that only Candida tenuis CBS 4435 was a good fermenter of both xylose and cellobiose under the test conditions used.  相似文献   
56.
The relationship between epithelial cell production and growth rate was investigated in Hydra attenuata under different feeding regimes. The increase of epithelial cell number was compared to the duration of the epithelial cell cycle using standard methods of cell cycle analysis. The results indicate that cell cycle changes accompanying changes in feeding regime are not sufficient to explain the altered growth rate. Under heavy feeding regimes, epithelial cell production equals tissue growth rate. At low feeding level or under starvation conditions the epithelial cell cycle lengthens and growth rate of epithelial cell population is slowed. However, the cell cycle changes are insufficient to account for the reduction in tissue growth and thus there is an effective overproduction of epithelial cells amounting to 10% per day. Evidence suggests that these excess cells are phagocytized by neighboring cells in the tissue. Thus phagocytosis is directly or indirectly involved in regulating the growth of hydra tissue.  相似文献   
57.
A simple three-enzyme treatment of collagenase, dispase and hyaluronidase on finely minced chick oviduct yields clumps of 50-150 cells. These cells attach to collagen-treated dishes and survive in culture for at least 2 weeks without subculturing. Oviduct cell cultures can also be induced to grow. Estradiol or epidermal growth factor (EGF) induce a 40% increase in cells in 4 days when cultures are grown in serum levels that do not support growth. Serum from estrogen-stimulated chicks promotes rapid cellular proliferation (doubling times of 1-2 days). Sera from estrogen withdrawn chicks, laying hen or horse do not support as rapid proliferation. The oviduct growth-promoting factors in serum from estrogen-stimulated chicks are not steroids or fibroblast growth factors (FGF). Removal of steroids from these sera by charcoal treatment or delipidization does not decrease the rate of growth. The addition of 1-100 nM estradiol does not increase a serum's ability to promote growth. Purified FGF or platelet-derived growth factor (PDGF) do not induce oviduct proliferation. These results were reproduced in oviduct cell cultures started from estrogen-stimulated and withdrawn chicks as well as laying hens. Thus the factors in serum from estrogen-stimulated chicks that promote rapid oviduct growth are induced by estrogen treatments in vivo, but do not seem to be only steroids.  相似文献   
58.
Single bilayer vesicles were prepared by sonication of 5 mol% 1-palmitoyl lysophosphatidylcholine and 95 mol% egg phosphatidylcholine. Incubation with lysophospholipase results in a fast hydrolysis of 80–90% of lysophosphatidylcholine. The remaining lysophosphatidylcholine is only very slowly hydrolysed. There results are interpreted as lysophosphatidylcholine being asymmetrically distributed over the two halves of the bilayer. The slow phase of lysophosphatidylcholine hydrolysis sets an upper limit to the rate of transbilayer movement of lysophosphatidylcholine. The half time of this process at 37° C is estimated to be about 100 h. Incorporation of cholesterol in the vesicles reduces the distributional asymmetry of lysophosphatidylcholine to the extent of an outside-inside ratio of 60 : 40. [14C]Lysophosphatidylcholine introduced into the outer monolayer of such vesicles by intervesicular transfer of lysophosphatidylcholine remains virtually completely available for hydrolysis by lysophospholipases, corroborating the interpretation that transbilayer movement of lysophosphatidylcholine in these vesicles is an extremely slow process.In handshaken liposomes consisting of 5 mol% 1-palmitoyl lysophosphatidylcholine and 95 mol% egg phosphatidylcholine 15–20% of lysophosphatidylcholine is readily available for exogenous lysophospholipase. This pool may represent lysophosphatidylcholine in the outer monolayer of the liposomes.  相似文献   
59.
A macerated human skull was subjected to orthodontic forces from 6.25 to 7.0 N per side. Double-exposure holographic interferograms (5 mW HeNe laser) were made frontally and oblique laterally. These were complemented with observations from a real time holographic interferogram. The displacements of the maxilla and the zygomatic bone were quantified. Special attention was paid to the reaction of the zygomaticomaxillary suture.  相似文献   
60.
We have identified a unique N-glycosylated Asn substitution for a Ser at position 434 of the A alpha chain of an abnormal fibrinogen designated fibrinogen Caracas II. This dysfibrinogen was characterized by impaired fibrin monomer aggregation. Since there were 4 Thr residues immediately following the mutation, a new Asn-X-Thr/Ser-type consensus sequence, Asn-Thr-Thr arose for N-glycosylation of the Asn. The extra oligosaccharide was found to consist mainly of a disialylated biantennary structure comprising 81.9%, while a neutral and a monosialylated biantennary oligosaccharide represented only 3.6% and 14.5%, respectively. The mutation resides in the carboxyl-terminal region of the A alpha chain, which could fold back to form an extra small globular region located near the central region of the molecule (Erickson, H.P., and Fowler, W.E. (1983) Ann. N. Y. Acad. Sci. 408, 146-163; Weisel, H.P., Stauffacher, C.V., Bullitt, E., and Cohen, C. (1985) Science 230, 3124-3133). Therefore, the participation of this region, referred to as an additional central domain or an alpha domain, in fibrin gel formation is strongly implicated.  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