全文获取类型
收费全文 | 97746篇 |
免费 | 8772篇 |
国内免费 | 247篇 |
专业分类
106765篇 |
出版年
2023年 | 388篇 |
2022年 | 880篇 |
2021年 | 1762篇 |
2020年 | 1011篇 |
2019年 | 1332篇 |
2018年 | 1618篇 |
2017年 | 1464篇 |
2016年 | 2365篇 |
2015年 | 4043篇 |
2014年 | 4576篇 |
2013年 | 5467篇 |
2012年 | 7280篇 |
2011年 | 7050篇 |
2010年 | 4509篇 |
2009年 | 4234篇 |
2008年 | 5976篇 |
2007年 | 6012篇 |
2006年 | 5598篇 |
2005年 | 5426篇 |
2004年 | 5217篇 |
2003年 | 5020篇 |
2002年 | 4718篇 |
2001年 | 1001篇 |
2000年 | 746篇 |
1999年 | 1025篇 |
1998年 | 1319篇 |
1997年 | 896篇 |
1996年 | 825篇 |
1995年 | 776篇 |
1994年 | 662篇 |
1993年 | 740篇 |
1992年 | 672篇 |
1991年 | 568篇 |
1990年 | 569篇 |
1989年 | 555篇 |
1988年 | 510篇 |
1987年 | 473篇 |
1986年 | 444篇 |
1985年 | 617篇 |
1984年 | 686篇 |
1983年 | 623篇 |
1982年 | 723篇 |
1981年 | 663篇 |
1980年 | 661篇 |
1979年 | 392篇 |
1978年 | 468篇 |
1977年 | 406篇 |
1976年 | 403篇 |
1974年 | 356篇 |
1973年 | 352篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
David W. Plath 《American anthropologist》1968,70(3):652-653
113.
114.
David A. Miller 《Journal of avian biology》2011,42(2):151-158
Adaptations that minimize the effects of stress are important components of avian development and have a role in structuring the relationship between development and fitness. I examined the effect of experimental manipulations of developmental stress during the nestling and fledgling stages on weight gain, growth in structural size, and take‐off flight speed of juvenile mourning doves Zenaida macroura. Brood size was manipulated during the nestling stage (≤11 days) and feeding rates during the fledgling stage (13–25 days) using a full factorial design. Effects of nutritional stress differed between the two treatments and depended on the response that was measured and the age at which it was measured. Treatment effects on flight ability were delayed and were greater for the treatment during the nestling stage than during the fledgling stage. Immediate treatment effects were greater than delayed effects on weight and size. Young were able to minimize effects of stress on flight ability at early ages when they would be most vulnerable to predation. However, by 90 days birds from enlarged broods were slower and flight time at 90 days was negatively correlated with weight and size at 25 days. There was no evidence for a cost of compensatory growth after experimental treatments ended on flight ability at 90 days. Results suggest that the effects of stress occur in a hierarchical manner across phenotypic components and that at early ages flight ability is prioritized through phenotypic plasticity. 相似文献
115.
Abstract: Phenylacetic acid, the major metabolite of phenylethylamine, has been identified and quantitated in rat brain regions by capillary column high-resolution gas chromatography mass spectrometry. Its distribution is heterogeneous and correlates with that of phenylethylamine. The values obtained were (ng/g ± SEM): whole brain, 31.2 ± 2.7; caudate nucleus, 64.6 ± 6.5; hypothalamus, 60.1 ± 7.4; cerebellum, 31.3 ± 2.9; brainstem, 33.1 ± 3.3, and the "rest," 27.6 ± 3.0. 相似文献
116.
A method for the isolation and concentration of the monoglutamate forms of folate cofactors from tissues and for their subsequent separation and quantitation using HPLC coupled with uv detection at 284 nm is described. A chromatographic procedure utilizing Dowex 50 has been developed for the separation of the folate monoglutamates from a large portion of the nonfolate-related material following digestion of the polyglutamated froms with a highly purified preparation of rat liver conjugase. This chromatographic procedure combined with concentration of the Dowex eluate by lyophilization eliminates uv-absorbing material, which interferes with the detection and quantitation of the folate cofactors and makes possible uv measurement of the individual folates. Reverse-phase paired-ion chromatography on μBondapak C18 coupled with uv detection allows direct quantitation of the folates in the nanogram range. 相似文献
117.
Anne M. Berry Eric M. Glare David Hansman James C. Paton 《FEMS microbiology letters》1989,65(3):275-278
Twenty-four of 63 enteric Gram-negative organisms (38.1%) which were isolated from 35 apparently healthy Nigerian students were found to have low trimethoprim resistance (MIC less than 1000 mg/l). These isolates were also found to be resistant to several other antibiotics and trimethoprim resistance was found to be transferable from 15 (62.5%) of the trimethoprim resistant organisms into E. coli EC 1005. It is likely that the high percentage of trimethoprim resistance encountered in this study is related to the high rate of resistance transfer which was observed. 相似文献
118.
John M. Robinson Sylvia A. Larrimore David W. Craft H.E. Heath Gary L. Sloan 《Biochemical and biophysical research communications》1982,109(3):730-737
The extracellular protease, endopeptidase, and hexosaminidase produced by were neither induced nor repressed by amino acids but required a tryptic digest of casein for their production. Catabolite repression of exoenzyme production by glucose was not affected by exogenous cyclic adenosine 3′, 5′-monophosphate but was partially relieved by di- or monobutyryl derivatives of this compound. 相似文献
119.
120.
A bioassay was developed by Rittschof el al. (1983) to examinedistance chemoreception in the predatory marine gastropod, Urosalpinxcinerea. This bioassay was used to test the effect of a senesof low mol. wt. organics on the ability of newly hatched oysterdrills to detect a prey odor released from barnacles, Balanusbalanoides. Two series of low mol. wt. organics were testedusing methanol as the reference compound. In one series, R-OH,the carbon chain length was varied from 1 to 4. In the secondseries, CH3-R, the chain length was held constant while thefunctional group, R, was varied. When these compounds were presentin the rnM range, they inhibited the creeping response of oysterdrills towards barnacle prey odor. In the CH3-R series, inhibitionincreased in the following order: sodium acetate > ethylacetate > acetonitnle > methanol; and, in the alcoholseries C1 to C4, inhibition increased with increasing chainlength. No creeping response was observed when these compoundswere tested in the absence of prey odor. 相似文献