全文获取类型
收费全文 | 414900篇 |
免费 | 52872篇 |
国内免费 | 191篇 |
出版年
2018年 | 3555篇 |
2016年 | 4627篇 |
2015年 | 6600篇 |
2014年 | 7620篇 |
2013年 | 11026篇 |
2012年 | 12233篇 |
2011年 | 12582篇 |
2010年 | 8450篇 |
2009年 | 7878篇 |
2008年 | 11107篇 |
2007年 | 11470篇 |
2006年 | 10665篇 |
2005年 | 10285篇 |
2004年 | 9934篇 |
2003年 | 9907篇 |
2002年 | 9519篇 |
2001年 | 19709篇 |
2000年 | 19917篇 |
1999年 | 15646篇 |
1998年 | 5337篇 |
1997年 | 5882篇 |
1996年 | 5567篇 |
1995年 | 5352篇 |
1994年 | 5252篇 |
1993年 | 5376篇 |
1992年 | 13343篇 |
1991年 | 13180篇 |
1990年 | 12554篇 |
1989年 | 12358篇 |
1988年 | 11273篇 |
1987年 | 10921篇 |
1986年 | 10203篇 |
1985年 | 10152篇 |
1984年 | 8497篇 |
1983年 | 7331篇 |
1982年 | 5641篇 |
1981年 | 5018篇 |
1980年 | 4835篇 |
1979年 | 7991篇 |
1978年 | 6391篇 |
1977年 | 5819篇 |
1976年 | 5479篇 |
1975年 | 6024篇 |
1974年 | 6219篇 |
1973年 | 6146篇 |
1972年 | 5550篇 |
1971年 | 5104篇 |
1970年 | 4257篇 |
1969年 | 4100篇 |
1968年 | 3676篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
991.
N Flomenberg K Welte R Mertelsmann N Kernan N Ciobanu S Venuta S Feldman G Kruger D Kirkpatrick B Dupont R O'Reilly 《Journal of immunology (Baltimore, Md. : 1950)》1983,130(6):2644-2650
Five children with primary deficiencies of T cell function were studied to assess the effects of highly purified exogenous Interleukin 2 (IL 2) on their in vitro T cell responses. The lymphocytes from one child with Nezelof's T cell deficiency demonstrated absence of endogenous IL 2 production and improved proliferative responses to mitogen or alloantigen in the presence of exogenous IL 2. Moreover, during in vitro mixed lymphocyte culture in the presence of exogenous IL 2, his lymphocytes were able to develop into cytotoxic effector cells. A second child with Nezelof's syndrome demonstrated a different type of defect. The lymphocytes from this child had less impairment of endogenous IL 2 production. Although IL 2 increased the proliferation of his cells in response to PHA, similar augmentation was not seen after stimulation with OKT3 or alloantigen. In cell-mediated cytotoxicity assays, after mixed lymphocyte culture, natural killer-like activity was strongly boosted in the cultures that contained IL 2, but T cell-mediated cytotoxicity was not. The lymphocytes from three patients with severe combined immunodeficiency did not show improved proliferative responses in the presence of IL 2. Thus, only one of the five patients demonstrated the combination of defective endogenous IL 2 production, but preservation of the ability to respond appropriately to exogenous IL 2. This child may therefore have suffered from a T cell defect pathophysiologically similar to that seen in nude or aged mice. 相似文献
992.
The technique of limited necropsy by histological examination of needle tissue cores obtained percutaneously is indicated when a full necropsy is not justified owing to the risk of infection or when tissue for special investigations is needed soon after death without recourse to full necropsy facilities. The method is ideal for detecting conditions producing diffuse changes in an organ. Because the cadaver is preserved essentially intact relatives who refuse permission for a standard necropsy might consent to a needle necropsy if this option is offered to them. 相似文献
993.
The neurotensin receptor protein, solubilized with digitonin/asolectin from bovine cerebral cortex membranes, was purified to apparent homogeneity by affinity chromatography using immobilized neurotensin. The product exhibits saturable and specific binding of [3,11-tyrosyl-3,5-3H]neurotensin with an apparent affinity (Kd = 5.5 nM) comparable to that measured in intact membranes and crude soluble extracts. The affinity-purified material, after reduction with 100 mM dithiothreitol, in denaturing gel electrophoresis showed a single polypeptide of Mr 72,000. Under nonreducing conditions the apparent Mr, however, was 50,000, suggesting the presence of intramolecular disulfide bonds. The purified neurotensin receptor was judged to be homogeneous, in that (i) only a single polypeptide was detectable; and (ii) the overall purification was 30,000-50,000-fold, giving a specific neurotensin-binding activity close to the theoretical maximum. 相似文献
994.
995.
Ahmed S. Abdel-Moneim Matthew D. Moore Mahmoud M. Naguib Jesus L. Romalde Maria S?derlund-Venermo 《中国病毒学》2020,35(2):248-252
The World Society for Virology (WSV) was founded and incorporated as a nonprofit organization in the United States in 2017. WSV seeks to strengthen and support both virological research and virologists who conduct research of viruses that affect humans, other animals, plants, and other organisms. One of the objectives of WSV is to connect virologists worldwide and support collaboration. Fulfilling this objective, virologists from fourteen countries in North America, Europe, Africa, Asia, and the Middle East met on 25–27th August 2019 in Stockholm, Sweden at the Karolinska University Hospital for the first Committee Meeting of WSV. This meeting included compelling keynote and honorary speeches and a series of 18 scientific talks were given encompassing a diverse array of subjects within virology. Followed by the scientific session, a business session was held where multiple aspects and next steps of the society were discussed and charted out. 相似文献
996.
Using mathematical modeling of the process of cancer treatment by the classical chemotherapy methods and therapy with biological agents, the effect of the kinetic parameters of the model on the final outcome of treatment was studied. It is established that the complete cure (i.e., the formation of a stable steady state with a zero number of cancer cells) cannot be reached by means of only classical chemotherapy. 相似文献
997.
Mousavi Shokouh Najafpour Ghasem D. Mohammadi Maedeh Seifi Mohammad Hasan 《Bioprocess and biosystems engineering》2018,41(4):519-530
Bioprocess and Biosystems Engineering - Cultivation of microalgae in wastewater is a promising and cost-effective approach for both CO2 biofixation and wastewater remediation. In this study, a new... 相似文献
998.
Four temperature-sensitive RNase P mutants were analyzed for the accumulation of 10 S RNA. In the 10 S region of the polyacrylamide gel two molecules appear, a and b. While the level of 10 Sa seems to be affected in some of the mutants, the 10 Sb molecule was not found in rnpB mutants. A plasmid (pL2), which contains Escherichia coli DNA sequences that complement, at least partially, rnp mutations, directs the synthesis of 10 Sb RNA. The presence of the pL2 plasmid complements the rnpA49, rnpB3187 and the rnpC241 mutations, as revealed by colony formation at “non-permissive” temperatures. However, the complementation of the rnpA49 mutation is much better than that of the other mutations. The complementation can also be measured by the increased level of RNase P activity in extracts. 10 Sa and b RNAs are unique among all RNAs tested thus far, since they are stable during exponential growth at 30 °C and 37 °C. However, at higher temperatures, such as 43 °C, the molecules are somewhat less stable, and they become rather labile when RNA synthesis is blocked by rifampicin. Structural analysis revealed that the 10 Sa and 10 Sb RNA molecules have dissimilar sequences. 相似文献
999.
1000.
Ong Jia Sin Taylor Todd D. Yong Cheng Chung Khoo Boon Yin Sasidharan Sreenivasan Choi Sy Bing Ohno Hiroshi Liong Min Tze 《Probiotics and antimicrobial proteins》2020,12(1):125-137
Probiotics and Antimicrobial Proteins - This study aimed to elucidate the targets and mechanisms of anti-staphylococcal effects from bioactive metabolites produced by lactic acid bacteria. We aimed... 相似文献