全文获取类型
收费全文 | 27261篇 |
免费 | 2387篇 |
国内免费 | 5篇 |
专业分类
29653篇 |
出版年
2023年 | 110篇 |
2022年 | 290篇 |
2021年 | 559篇 |
2020年 | 303篇 |
2019年 | 403篇 |
2018年 | 518篇 |
2017年 | 434篇 |
2016年 | 790篇 |
2015年 | 1264篇 |
2014年 | 1430篇 |
2013年 | 1731篇 |
2012年 | 2175篇 |
2011年 | 2051篇 |
2010年 | 1317篇 |
2009年 | 1147篇 |
2008年 | 1586篇 |
2007年 | 1604篇 |
2006年 | 1438篇 |
2005年 | 1335篇 |
2004年 | 1351篇 |
2003年 | 1214篇 |
2002年 | 1178篇 |
2001年 | 379篇 |
2000年 | 320篇 |
1999年 | 301篇 |
1998年 | 318篇 |
1997年 | 225篇 |
1996年 | 225篇 |
1995年 | 185篇 |
1994年 | 175篇 |
1993年 | 169篇 |
1992年 | 178篇 |
1991年 | 174篇 |
1990年 | 178篇 |
1989年 | 140篇 |
1988年 | 143篇 |
1987年 | 145篇 |
1986年 | 136篇 |
1985年 | 134篇 |
1984年 | 106篇 |
1983年 | 118篇 |
1982年 | 101篇 |
1981年 | 99篇 |
1980年 | 85篇 |
1979年 | 92篇 |
1978年 | 113篇 |
1977年 | 86篇 |
1976年 | 74篇 |
1975年 | 73篇 |
1973年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
A newborn child was noted to have an ulcerated lesion on the vertex of her scalp, which was diagnosed as aplasia cutis congenita. As this disorder is relatively rare and frequently misdiagnosed, this case is reported and the relevant literature reviewed. 相似文献
3.
Thorsten Thye Genevieve Scarisbrick Edmund N. L. Browne Margaret Amanua Chinbuah John Gyapong Ivy Osei Ellis Owusu-Dabo Stefan Niemann Sabine Rüsch-Gerdes Christian G. Meyer Rolf D. Horstmann 《PloS one》2009,4(7)
The gene of Cytotoxic T Lymphocyte-associated Antigen 4 (CTLA4), a negative regulator of T lymphocytes, contains a single-nucleotide polymorphism (SNP) at position +6230A->G (ct60A->G), which has been found associated with several autoimmune diseases and appears to reduce T-cell inhibitory activity. In Ghana, West Africa, we compared the frequencies of CTLA4 +6230 A/G and 6 haplotype-tagging SNPs in 2010 smear-positive, HIV-negative patients with pulmonary tuberculosis (TB) and 2346 controls matched for age, gender and ethnicity. We found no difference in allele frequencies between cases and controls. However, +6230A and a distinct CTLA4 haplotype and a diplotype comprising the +6230A allele were significantly less frequent among cases with large opacities in chest radiographs compared to those with small ones (Pcorrected [cor] = 0.002, Pcor = 0.00045, P = 0.0005, respectively). This finding suggests that an increased T-cell activity associated with the CTLA4 +6230G allele contributes to pathology rather than to protection in pulmonary TB. 相似文献
4.
Despite considerable progress in recent years in the promotion of flowering in conifers, relatively little is known about the endogenous control of sex expression or its practical manipulation to aid pollen and crop management in seed orchards. Well defined patterns of sexual zonation exist within the tree crown and shoot, and these appear to be associated with hormonal and possibly nutritional gradients. No firm conclusions, however, are possible regarding the specific role(s) of different PGRs in sex expression, this being as much as a problem of lack of critical study as the complexity of the process itself. Whether a PGR such as gibberellins or auxins, or a cultural treatment that itself may influence endogenous hormone levels, primarily promotes female or male flowering often depends on the position within the crown of the shoot being treated, and its timing in relation to stage of primordia development. Photoperiod also may be involved- short days favoring females and long days males, at least in some species- although its role in controlling sex expression is by no means clear. Practical manipulation of sex expression may be possible through selective crown pruning, different PGR combinations, treatment timing and/or photoperiod control, but the development of such techniques for operational use will require a better basic understanding of the endogenous regulatory mechanisms involved. 相似文献
5.
6.
7.
Jill S. Marty James P. Higham Elizabeth L. Gadsby Caroline Ross 《International journal of primatology》2009,30(6):807-823
Sexual selection has driven the evolution and elaboration of a wide variety of displays and ornaments in male nonhuman primates,
including capes, cheek flanges, and sexual coloration. Among the most sexually dimorphic of all primates is the drill (Mandrillus leucophaeus), the males of which can be 3 times the mass of females, possess large canines, and exhibit extremely bright sexual skin
coloration. However, the function of male coloration in this species has never been examined. Here, we present data on male
color (measured objectively using digital photography), dominance rank, measures of male-female association, and key sexual
behaviors, of adult male drills (n = 17) living in four semi free-ranging enclosures at the Drill Rehabilitation and Breeding Center in Nigeria. We test the
hypothesis that male coloration is a badge of status, indicating dominance rank, and the hypothesis that male coloration attracts
females. We found that male coloration did indicate rank, and that high ranking, strongly colored males were more likely to
associate with adult females, and more specifically with fully tumescent females. These males also engaged in more sexual
activity. However, measures of male-female association and sexual behaviors were not related to male color once rank had been
taken into consideration; i.e., for males of a given rank, females did not prefer those that were more colorful. We discuss
the results in light of what is known about the wild drill social system, in which unfamiliar individuals may come together
in “supergroups,” and in which quality indicators of competitive ability may be particularly important. 相似文献
8.
Se-Chan Kim Alexander Ghanem Heidi Stapel Klaus Tiemann Pascal Knuefermann Andreas Hoeft Rainer Meyer Christian Grohé Anne A Knowlton Georg Baumgarten 《BMC physiology》2007,7(1):5
Backgound
It has been reported that Toll-like receptor 4 (TLR4) deficiency reduces infarct size after myocardial ischemia/reperfusion (MI/R). However, measurement of MI/R injury was limited and did not include cardiac function. In a chronic closed-chest model we assessed whether cardiac function is preserved in TLR4-deficient mice (C3H/HeJ) following MI/R, and whether myocardial and systemic cytokine expression differed compared to wild type (WT). 相似文献9.
10.
Characterization of sequential immune complexes in infective endocarditis by Western blot analysis 总被引:2,自引:0,他引:2
R D Inman R A Rosenberg P B Redecha C L Christian 《Journal of immunology (Baltimore, Md. : 1950)》1984,133(1):217-221
A patient with cutaneous vasculitis during infective endocarditis due to Lactobacillus casei was studied. Immune complexes (IC) were isolated from serum at the time of diagnosis and after 4 wk of therapy. Purification of IC used differential polyethylene glycol precipitation and competitive binding to staphylococcal protein A. In situ radioiodination of IC was performed, followed by SDS-polyacrylamide gel electrophoresis (PAGE). Anti-IC antisera were raised in rabbits by immunization with purified IC. IC were characterized by SDS-PAGE followed by electrophoretic transfer to nitrocellulose, incubation with antiserum and then with 125I protein A, and autoradiography. Although early and late IC differed quantitatively, there were no differentiating immunochemical features. Both IC contained a 60,000 dalton component that did not react with preimmune serum nor with anti-normal human serum. This component reacted with antiserum rendered specific for L. casei by affinity chromatography. The restricted antigen-antibody representation in IC contrasted with a wider panel of antibody activity in patient serum. The Western blot analysis proves to be an ideal method for the characterization of IC because of its sensitivity, dissociative capability, and preservation of immunoreactivity. IC isolated at a time removed from the original antigenic challenge may provide insight into the nature of the inciting antigen. 相似文献