全文获取类型
收费全文 | 53696篇 |
免费 | 5133篇 |
国内免费 | 30篇 |
出版年
2023年 | 172篇 |
2021年 | 639篇 |
2020年 | 532篇 |
2019年 | 693篇 |
2018年 | 861篇 |
2017年 | 795篇 |
2016年 | 1345篇 |
2015年 | 2242篇 |
2014年 | 2366篇 |
2013年 | 3132篇 |
2012年 | 3658篇 |
2011年 | 3659篇 |
2010年 | 2439篇 |
2009年 | 2098篇 |
2008年 | 3055篇 |
2007年 | 3064篇 |
2006年 | 2812篇 |
2005年 | 2919篇 |
2004年 | 2843篇 |
2003年 | 2782篇 |
2002年 | 2732篇 |
2001年 | 612篇 |
2000年 | 497篇 |
1999年 | 620篇 |
1998年 | 750篇 |
1997年 | 543篇 |
1996年 | 496篇 |
1995年 | 521篇 |
1994年 | 468篇 |
1993年 | 427篇 |
1992年 | 508篇 |
1991年 | 425篇 |
1990年 | 359篇 |
1989年 | 362篇 |
1988年 | 341篇 |
1987年 | 330篇 |
1986年 | 308篇 |
1985年 | 395篇 |
1984年 | 419篇 |
1983年 | 335篇 |
1982年 | 450篇 |
1981年 | 393篇 |
1980年 | 342篇 |
1979年 | 279篇 |
1978年 | 311篇 |
1977年 | 286篇 |
1976年 | 258篇 |
1975年 | 213篇 |
1974年 | 259篇 |
1973年 | 259篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
Jean L. Santos Paulo R. Yamasaki Chung Man Chin Célio H. Takashi Fernando R. Pavan Clarice Q.F. Leite 《Bioorganic & medicinal chemistry》2009,17(11):3795-3799
New phthalimide derivatives were easily prepared through condensation of phthalic anhydride and selected amines with variable yields (70–90%). All compounds (3a–l) were evaluated against Mycobacterium tuberculosis H37Rv using Alamar Blue susceptibility. The compounds 3c, 3i, and 3l have the minimum inhibitory concentrations (MICs) of 3.9, 7.8, and 5.0 μg/mL, respectively, and could be considered new lead compounds in the treatment of tuberculosis and multi-drug resistant tuberculosis. 相似文献
73.
Erica N. Spotswood Jean‐Yves Meyer James W. Bartolome 《Journal of Biogeography》2012,39(11):2007-2020
Aim We studied how the abundance of the highly invasive fruit‐bearing tree Miconia calvescens DC. influences seed dispersal networks and the foraging patterns of three avian frugivores. Location Tahiti and Moorea, French Polynesia. Methods Our study was conducted at six sites which vary in the abundance of M. calvescens. We used dietary data from three frugivores (two introduced, one endemic) to determine whether patterns of fruit consumption are related to invasive tree abundance. We constructed seed dispersal networks for each island to evaluate how patterns of interaction between frugivores and plants shift at highly invaded sites. Results Two frugivores increased consumption of M. calvescens fruit at highly invaded sites and decreased consumption of other dietary items. The endemic fruit dove, Ptilinopus purpuratus, consumed more native fruit than either of the two introduced frugivores (the red‐vented bulbul, Pycnonotus cafer, and the silvereye, Zosterops lateralis), and introduced frugivores showed a low potential to act as dispersers of native plants. Network patterns on the highly invaded island of Tahiti were dominated by introduced plants and birds, which were responsible for the majority of plant–frugivore interactions. Main conclusions Shifts in the diet of introduced birds, coupled with reduced populations of endemic frugivores, caused differences in properties of the seed dispersal network on the island of Tahiti compared to the less invaded island of Moorea. These results demonstrate that the presence of invasive fruit‐bearing plants and introduced frugivores can alter seed dispersal networks, and that the patterns of alteration depend both on the frugivore community and on the relative abundance of available fruit. 相似文献
74.
75.
76.
77.
78.
Jean Lafuste 《Geobios》1979,12(3):353-363
The microstructure of two species of Cladochonusfrom Algerian Carboniferous, C. crassus (McCoy) and C. cf. tenuicollisMcCoy, has been studied by ultra-thin sections. Their walls consist of: 1. an external fibrous layer, 2. a median layer of undulating lamellae, 3. an internal zone of slender, elongated elements to which the name of «grundulae is given here. New data bring complements to the generic diagnosis of Cladochonus s. str. Some Permian cladochonid forms show different microstructures and should, therefore, be shifted to new generic units. 相似文献
79.
Laticifers of Papaver bracteatum Lindl., population Arya II, seedlings were examined by electron microscopy. Laticifers were first differentiated in procambium of the radicle associated with phloem about 72 hr after seeds were sown. Proliferation of membrane-bound vesicles of apparent endoplasmic reticulum origin distinguished laticifers from adjacent cells. Vesicles developed electron-dense caps from the internal condensation of small particles. Laticifer initials possessed the usual complement of organelles that became obscured in mature cells by the large, closely packed vesicles. Plastids contained an electron-dense, membrane-bound inclusion, but never developed lamellae or starch grains. Articulation and anastomoses between laticifer elements resulted from gradual removal of wall materials by both cells on opposite sides of the common walls at a perforation site. Differentiation of the laticifer initials and the micromorphology of the protoplast of P. bracteatum is similar to that reported for P. somniferum. 相似文献
80.