全文获取类型
收费全文 | 47119篇 |
免费 | 3520篇 |
国内免费 | 6343篇 |
出版年
2024年 | 208篇 |
2023年 | 953篇 |
2022年 | 1284篇 |
2021年 | 1524篇 |
2020年 | 1508篇 |
2019年 | 2099篇 |
2018年 | 1694篇 |
2017年 | 1564篇 |
2016年 | 1598篇 |
2015年 | 1484篇 |
2014年 | 2268篇 |
2013年 | 3220篇 |
2012年 | 1926篇 |
2011年 | 2139篇 |
2010年 | 1687篇 |
2009年 | 2276篇 |
2008年 | 2319篇 |
2007年 | 2452篇 |
2006年 | 2208篇 |
2005年 | 1995篇 |
2004年 | 1725篇 |
2003年 | 1640篇 |
2002年 | 1472篇 |
2001年 | 1176篇 |
2000年 | 1059篇 |
1999年 | 1027篇 |
1998年 | 937篇 |
1997年 | 799篇 |
1996年 | 721篇 |
1995年 | 687篇 |
1994年 | 691篇 |
1993年 | 634篇 |
1992年 | 591篇 |
1991年 | 601篇 |
1990年 | 471篇 |
1989年 | 413篇 |
1988年 | 435篇 |
1987年 | 349篇 |
1986年 | 379篇 |
1985年 | 571篇 |
1984年 | 665篇 |
1983年 | 384篇 |
1982年 | 517篇 |
1981年 | 498篇 |
1980年 | 435篇 |
1979年 | 323篇 |
1978年 | 236篇 |
1977年 | 247篇 |
1976年 | 233篇 |
1973年 | 183篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
A bacterial clone carrying sequences coding for elongation factor EF-1 alpha from Artemia 总被引:2,自引:0,他引:2
A bacterial cDNA clone was identified carrying one third of the nucleotides coding for elongation factor EF-1 alpha from the brine shrimp Artemia. The sequence of codons corresponds with the known sequence of amino acids of EF-1 alpha in the region involved. 相似文献
73.
74.
An examination of four species of Cirsium disclosed the presence of two new flavonoids in C. lineare. The structure of one was 5,4′-dihydroxy-6,7,3′-trimethoxyflavone (cirsilineol) 4′-monoglucoside and the other 5,3′,4′-trihydroxy-6,7-dimethoxyflavone (cirsiliol) 4′-monoglucoside. Luteolin 7-glucoside was found in C. suffultum, and pectolinarin and linarin in C. kamtschaticum and C. pectinellum. 相似文献
75.
76.
《Journal of biological dynamics》2013,7(4):318-334
In this paper, we study a two-species competitive system where both the species produce toxin against each other at some cost to their growth rates. A much wider set of outcomes is possible for our system. These outcomes are important contrasts to competitive exclusion or bistable attractors that are often the outcomes for competitive systems. We show that toxin helps to gain an advantage in competition for toxic species whenever the cost of toxin production remains within some moderate value; otherwise it may result in the extinction of the species itself. 相似文献
77.
Liane Wehder Günther Ernst Anna C. Crecelius Orlando Guntinas-Lichius Christian Melle Ulrich S. Schubert Ferdinand von Eggeling 《The journal of histochemistry and cytochemistry》2010,58(10):929-937
Carcinoma tissue consists of not only tumor cells but also fibroblasts, endothelial cells or vascular structures, and inflammatory cells forming the supportive tumor stroma. Therefore, the spatial distribution of proteins that promote growth and proliferation in these complex functional units is of high interest. Matrix-assisted laser desorption/ionization imaging mass spectrometry is a newly developed technique that generates spatially resolved profiles of protein signals directly from thin tissue sections. Surface-enhanced laser desorption/ionization mass spectrometry (MS)combined with tissue microdissection allows analysis of defined parts of the tissue with a higher sensitivity and a broader mass range. Nevertheless, both MS-based techniques have a limited spatial resolution. IHC is a technique that allows a resolution down to the subcellular level. However, the detection and measurement of a specific protein expression level is possible only by semiquantitative methods. Moreover, prior knowledge about the identity of the proteins of interest is necessary. In this study, we combined all three techniques to gain highest spatial resolution, sensitivity, and quantitative information. We used frozen tissue from head and neck tumors and chose two exemplary proteins (HNP1–3 and S100A8) to highlight the advantages and disadvantages of each technique. It could be shown that the combination of these three techniques results in congruent but also synergetic data. (J Histochem Cytochem 58:929–937, 2010) 相似文献
78.
Pablo Manrique-Saide Sergio Ibáñez-Bernal Hugo Delfín-González Victor Parra Tabla 《Medical and veterinary entomology》1998,12(4):386-390
Abstract .The effect of the introduction of the entomophagous copepod Mesocyclops longisetus (Acuacultura F.C.B. strain) on the survival of Aedes aegypti immature stages in car tyres was evaluated under semi-natural conditions in the municipality of Merida, Yucatan, Mexico. Life tables were constructed for the immature stages of the mosquito in the presence and absence of M. longisetus , and the survival data were compared using log–linear models. The data set was adjusted using the GLIM statistical package and the quality of adjustment was evaluated with a chi-squared test . Survivorship curves were constructed for each treatment.
In the absence of M. longisetus , the survivorship of Ae. aegypti immature stages averaged 9%. The highest mortality rate was observed during the fourth larval instar (54%) and the resulting survival pattern corresponded to a type II survivorship curve. The mortality rate of Ae. aegypti first-instar larvae (fifty per tyre) increased more than 200-fold in the presence of M. longisetus (twenty per tyre) and the highest mortality was during the first two larval instars, where it reached 98.9%, with a resulting survivorship of 0.2%. Overall mortality was sixfold greater in the presence of the copepod than in its absence. The survival pattern of immature stages of Ae. aegypti in the presence of the copepod corresponded to a type III survivorship curve. As M. longisetus was so effective against Ae. aegypti immature stages in tyres under semi-natural conditions, its long-term effectiveness should be evaluated under socially and ecologically realistic field conditions in Mexico. 相似文献
In the absence of M. longisetus , the survivorship of Ae. aegypti immature stages averaged 9%. The highest mortality rate was observed during the fourth larval instar (54%) and the resulting survival pattern corresponded to a type II survivorship curve. The mortality rate of Ae. aegypti first-instar larvae (fifty per tyre) increased more than 200-fold in the presence of M. longisetus (twenty per tyre) and the highest mortality was during the first two larval instars, where it reached 98.9%, with a resulting survivorship of 0.2%. Overall mortality was sixfold greater in the presence of the copepod than in its absence. The survival pattern of immature stages of Ae. aegypti in the presence of the copepod corresponded to a type III survivorship curve. As M. longisetus was so effective against Ae. aegypti immature stages in tyres under semi-natural conditions, its long-term effectiveness should be evaluated under socially and ecologically realistic field conditions in Mexico. 相似文献
79.
M. A. PEIRCE 《The Journal of eukaryotic microbiology》1973,20(5):543-546
An avian piroplasm, Nuttallia balearicae sp. n., is described from captive Balearica p. pavonina and B. p. gibbericeps. Other avian piroplasms and their validity and taxonomic status are discussed. The possible route of transmission of these parasites is also considered. 相似文献
80.