全文获取类型
收费全文 | 13357篇 |
免费 | 1062篇 |
国内免费 | 1篇 |
专业分类
14420篇 |
出版年
2023年 | 47篇 |
2022年 | 130篇 |
2021年 | 273篇 |
2020年 | 133篇 |
2019年 | 185篇 |
2018年 | 235篇 |
2017年 | 200篇 |
2016年 | 352篇 |
2015年 | 560篇 |
2014年 | 635篇 |
2013年 | 767篇 |
2012年 | 965篇 |
2011年 | 929篇 |
2010年 | 583篇 |
2009年 | 539篇 |
2008年 | 732篇 |
2007年 | 770篇 |
2006年 | 721篇 |
2005年 | 717篇 |
2004年 | 691篇 |
2003年 | 659篇 |
2002年 | 624篇 |
2001年 | 262篇 |
2000年 | 254篇 |
1999年 | 259篇 |
1998年 | 184篇 |
1997年 | 139篇 |
1996年 | 111篇 |
1995年 | 100篇 |
1994年 | 83篇 |
1993年 | 84篇 |
1992年 | 124篇 |
1991年 | 136篇 |
1990年 | 134篇 |
1989年 | 121篇 |
1988年 | 109篇 |
1987年 | 100篇 |
1986年 | 93篇 |
1985年 | 93篇 |
1984年 | 78篇 |
1983年 | 75篇 |
1982年 | 45篇 |
1981年 | 34篇 |
1979年 | 46篇 |
1978年 | 32篇 |
1977年 | 33篇 |
1976年 | 24篇 |
1975年 | 22篇 |
1974年 | 26篇 |
1973年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Dr. John L. Johnson Carol Phelps Lisa Barroso Mary D. Roberts David M. Lyerly Tracy D. Wilkins 《Current microbiology》1990,20(6):397-401
Results from our cloning studies on toxin A indicated that the gene for toxin B resided approximately 1 kb upstream of the toxin A gene. Clone pCD19, which contains the 5-end of the toxin A gene and a small open reading frame, was found to contain 1.2 kb of DNA which, when subcloned, expressed a nontoxic peptide that reacted with toxin B antibodies. The rest of the toxin B gene was located on the 6.8 kb cloned fragment of plasmid pCD19L. The two fragments overlapped 0.8 kb. Lysates containing protein expressed by the 6.8 fragment were cytotoxic and lethal, and were neutralized by toxin B antibody. The two fragments were ligated to give the complete toxin B gene. The protein expressed by the complete gene was cytotoxic and lethal, and showed complete immunological identity with toxin B. Further analysis of the expressed protein and the toxin B gene confirmed our earlier findings showing that toxin B has a molecular weight of 240,000 or greater. 相似文献
43.
Summary Methotrexate (MTX) was conjugated to an anti-carcinoembryonic antigen monoclonal antibody (NP2) by using amino-dextran as an intermediate carrier. The drug was chemically linked to amino-dextran (averageM
r = 40000), and the resulting MTX-dextran was then site-specifically attached to the carbohydrate moiety of the antibody. Athymic nude mice that carried human colonic GW-39 tumors (s. c.) were treated with the immunoconjugate. In this study, the specific conjugate caused a greater inhibition of the tumor growth than either free MTX or its conjugate with dextran and an irrelevant antibody. The intermediate MTX-dextran and the unlinked mixture of MTX-dextran with NP2 were both relatively ineffective in inhibiting tumor growth. The greatly reduced host toxicity permitted the use of the MTX-dextran-NP2 in a high-dose therapy of this tumor system.Supported in part by U.S.P.H.S. grant CA39 841 from the NIH 相似文献
44.
Richard R. Keen Lisa A. Stella D. Preston Flanigan William E. M. Lands 《Free radical biology & medicine》1990,9(6):485-494
Fatty acid hydroperoxides in the plasma of 18 patients who were undergoing normal postoperative periods following major thoracic or abdominal operations were measured by using a sensitive assay based upon the activation of the cyclooxygenase activity of prostaglandin H synthase. Following major thoracic operations of nine patients, the mean difference between the arterial (0.49 ± 0.13 μM, mean ± S.E.M.) and mixed venous (−0.09 ± 0.12 μM) level of hydroperoxide was 0.58 ± 0.13 μM (p < 0.01). In marked contrast to this result, major abdominal operations of nine patients led to a mean difference between the arterial (−0.19 ± 0.16 μM) and mixed venous (0.46 ± 0.08 μM) hydroperoxide levels of −0.65 ± 0.17 μM (p < 0.01). Both pulmonary and intraabdominal tissues appear capable of generating significant amounts of fatty acid hydroperoxide in response to standard surgical procedures. The A-MV differences suggest that the blood-borne hydroperoxides were rapidly cleared from the circulation by tissue capillary beds. 相似文献
45.
Kunio Yonemasu Takako Sasaki Yoshiko Dohi Charles M. Lapière Betty Nusgens 《生物化学与生物物理学报:疾病的分子基础》1990,1096(1):47-51
C1q, a collagen-like complement protein, was purified from the serum of a ddermatosparactic calf which lacks procollagen N-terminal proteinase (pN-proteinase). The specific hemolytic activity of the serum Clq from the dermatosparactic animal was identical to that of C1q from a normal calf. Gel-filtration of serum from dermatosparactic calf, on Sepharose 6B, showed the presence of C1q-antigenic material at only one position which was identical to the elution position of normal bovine C1q. No differdence, under dissociating conditions, could be seen in the size of the chains of C1q in specific immunoprecipitates isolated from the sera of dermatosparactic and normal animals, as judged by polyacrylamidegel electrophoresis (PAGE) in the presence of sodium dodecyl sulfate (SDS). The C1q from the dermatosparactic animal showed the same N-terminal amino acid and typtic-digest peptide pattern on HPLC as C1q from the normal calf. These results strongly suggest that pN-proteinase is not involved in the extracellular processing of C1q. 相似文献
46.
47.
Types,rates, origin and expressivity of chromosome mutations involving 13q14 in retinoblastoma patients 总被引:7,自引:2,他引:5
Summary A cytogenetic survey of 200 retinoblastoma (Rb) patients revealed that approximately 8.5% of the fresh germinal mutations were microscopically detectable chromosome mutations, either interstitial deletions or rearrangements, involving 13q14. They showed a strong bias toward paternal origin, indicating a significant contribution of errors in paternal meiotic processes. The incidence of patients with Rb due to such chromosome mutations was estimated to be 1.9 x 10-6 of live births. Age-specific incidence of Rb tumors suggested that the Rb mutations by such chromosomal mechanisms had a lower carcinogenic potential, as indicated by the later onset of disease, than other Rb mutations of germinal origin. 相似文献
48.
The light-induced increase in chloroplast DNA was not inhibited by two inhibitors of protein synthesis on 70S polysomes, chloramphenicol and lincomycin, in greening pea leaves. The changes in chloroplast DNA were observed by fluorescence microscopy and measured by hybridization to specific cloned probes. The results suggest that the light-induced increase in chloroplast DNA proceeds without de novo protein synthesis in the chloroplast, in agreement with those with mutants and cultured leaf tissue. 相似文献
49.
50.
Sallie W. Chisholm Sheila L. Frankel Ralf Goericke Robert J. Olson Brian Palenik John B. Waterbury Lisa West-Johnsrud Erik R. Zettler 《Archives of microbiology》1992,157(3):297-300
Several years ago, prochlorophyte picoplankton were discovered in the N. Atlantic. They have since been found to be abundant within the euphotic zone of the world's tropical and temperate oceans. The cells are extremely small, lack phycobiliproteins, and contain divinyl chlorophyll a and b as their primary photosynthetic pigments. Phylogenies constructed from DNA sequence data indicate that these cells are more closely related to a cluster of marine cyanobacteria than to their prochlorophyte relatives Prochlorothrix and Prochloron. Several strains of this organism have recently been brought into culture, and herewith are given the name Prochlorococcus marinus. 相似文献