全文获取类型
收费全文 | 52977篇 |
免费 | 3689篇 |
国内免费 | 5854篇 |
出版年
2024年 | 228篇 |
2023年 | 1036篇 |
2022年 | 1441篇 |
2021年 | 1780篇 |
2020年 | 1764篇 |
2019年 | 2515篇 |
2018年 | 2032篇 |
2017年 | 1656篇 |
2016年 | 1591篇 |
2015年 | 1666篇 |
2014年 | 2867篇 |
2013年 | 3811篇 |
2012年 | 2241篇 |
2011年 | 2754篇 |
2010年 | 2076篇 |
2009年 | 2435篇 |
2008年 | 2521篇 |
2007年 | 2687篇 |
2006年 | 2343篇 |
2005年 | 2133篇 |
2004年 | 1840篇 |
2003年 | 1707篇 |
2002年 | 1528篇 |
2001年 | 1126篇 |
2000年 | 1031篇 |
1999年 | 960篇 |
1998年 | 902篇 |
1997年 | 790篇 |
1996年 | 709篇 |
1995年 | 647篇 |
1994年 | 648篇 |
1993年 | 561篇 |
1992年 | 555篇 |
1991年 | 571篇 |
1990年 | 433篇 |
1989年 | 425篇 |
1988年 | 411篇 |
1987年 | 362篇 |
1986年 | 394篇 |
1985年 | 621篇 |
1984年 | 729篇 |
1983年 | 431篇 |
1982年 | 591篇 |
1981年 | 560篇 |
1980年 | 498篇 |
1979年 | 371篇 |
1978年 | 275篇 |
1977年 | 279篇 |
1976年 | 254篇 |
1973年 | 198篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
Several aspects of a diel vertical migration (DVM) of adultEudiaptomus gracilis in Lake Maarsseveen (The Netherlands) are described. The period of DVM lasted from the end of May until the middle of August. On May 21, 1989, the population was found divided into a deep dwelling part and a part in the upper five meter. Large shoals of juvenile perch were observed in the open water for the first time. On June 7, the whole population was down below 10 m and concentrated in a zone of high chlorphyll-a concentrations. One week later, a regular DVM was performed. The amplitude of this migration gradually decreased towards the end of the migration period. The ascent in the evening and the descent in the morning took place after sunset and before sunrise, respectively. The movements coincided with high relative changes in light intensity. Population size increased rapidly during the period of DVM but decreased again before the end of this period. 相似文献
112.
A. S. Davydov 《Journal of biological physics》1991,18(2):111-125
The lifetime of Davydov solitons in a one-dimensional system is studied theoretically. The process of thermalization and the properties of solitons at finite temperature are investigated and the processes of soliton creation and disintegration are discussed. 相似文献
113.
Long-term assessments of species assemblages are valuable tools for detecting species ecological preferences and their dispersal
tracks, as well as for assessing the possible effects of alien species on native communities. Here we report a 50-year-long
study on population dynamics of the four species of land flatworms (Platyhelminthes, Tricladida, Terricola) that have colonized
or become extinct in a 70-year-old Atlantic Forest regrowth remnant through the period 1955–2006. On the one hand, the two
initially most abundant species, which are native to the study site, Notogynaphallia
ernesti and Geoplana multicolor have declined over decades and at present do not exist in the forest remnant. The extinction of these species is most likely
related with their preference for open vegetation areas, which presently do not exist in the forest remnant. On the other
hand, the neotropical Geoplaninae 1 and the exotic Endeavouria septemlineata were detected in the forest only very recently. The long-term study allowed us to conclude that Geoplaninae 1 was introduced
into the study area, although it is only known from the study site. Endeavouria septemlineata, an active predator of the exotic giant African snail, is originally known from Hawaii. This land flatworm species was observed
repeatedly in Brazilian anthropogenic areas, and this is the first report of the species in relatively well preserved native
forest, which may be evidence of an ongoing adaptive process. Monitoring of its geographic spread and its ecological role
would be a good practice for preventing potential damaging effects, since it also feeds on native mollusk fauna, as we observed
in lab conditions.
Júlio Pedroni: Granted by CNPQ–Brazil. 相似文献
114.
115.
《Critical reviews in biotechnology》2013,33(1):40-48
The availability of binders to different functional domains of the same protein or to physiologically co-operating proteins allows for the simultaneous inhibition of independent downstream signaling pathways. This multi-target approach represents a promising therapeutic strategy, as demonstrated in the case of the synergistic effect of anti-Her2 treatment based on the combined use of the trastuzumab and pertuzumab monoclonal antibodies that induce cellular cytotoxicity and impair the receptor dimerization, respectively. Therefore, a reliable selection method for the recovery of epitope-specific antibodies is highly needed. Animal immunization with short peptides resembling the epitope sequence for raising conventional antibodies represents an alternative. Panning phage displayed libraries of recombinant antibodies such as scFvs and nanobodies or of other peptide collections is another option. Although recombinant antibodies can provide the same specificity as conventional antibodies, they offer at least two further advantages: i) the protocols for the selection of epitope-specific antibodies can be rationally designed, and ii) their expression as multivalent, bispecific and biparatopic molecules is feasible. This review will analyze the recent literature concerning technical aspects related to the isolation, the expression as multivalent molecules, and the therapeutic applications of binders able to interfere with antigen functional domains. The term binder will be preferred when possible to include those molecules, such as peptides or affibodies, with at least some proven practical uses. 相似文献
116.
117.
118.
119.
Tamanna Jahangir 《Journal of enzyme inhibition and medicinal chemistry》2013,28(6):888-894
In the present study we have evaluated the antigenotoxic effects of Farnesol (FL) a 15-carbon isoprenoid alcohol against benzo (a) pyrene [B(a)P] (125 mg kg? 1.b.wt oral) induced toxicity. B(a)P administration lead to significant induction in Cytochrome P450 (CYP) content and aryl hydrocarbon hydrolase (AHH) activity (p < 0.001), DNA strand breaks and DNA adducts (p < 0.001) formation. FL was shown to suppress the activities of both CYP and AHH (p < 0.005) in modulator groups. FL pretreatment significantly (p < 0.001) restored depleted levels of reduced glutathione (GSH), quinone reductase (QR) and glutathione –S-transferase (GST). A simultaneous significant and at both the doses reduction was seen in DNA strand breaks and in in-vivo DNA adducts formation (p < 0.005), which gives some insight on restoration of DNA integrity. The results support the protective nature of FL. Hence present data supports FL as a future drug to preclude B (a) P induced toxicity. 相似文献
120.
Intrinsic processes are assumed to underlie life history expression and trade‐offs, but extrinsic inputs are theorised to shift trait expression and mask trade‐offs within species. Here, we explore application of this theory across species. We do this based on parentally induced embryo temperature as an extrinsic input, and mass‐specific embryo metabolism as an intrinsic process, underlying embryonic development rate. We found that embryonic metabolism followed intrinsic allometry rules among 49 songbird species from temperate and tropical sites. Extrinsic inputs via parentally induced temperatures explained the majority of variation in development rates and masked a relationship with metabolism; metabolism explained a minor proportion of the variation in development rates among species, and only after accounting for temperature effects. We discuss evidence that temperature further obscures the expected interspecific trade‐off between development rate and offspring quality. These results demonstrate the importance of considering extrinsic inputs to trait expression and trade‐offs across species. 相似文献