全文获取类型
收费全文 | 3052篇 |
免费 | 282篇 |
出版年
2021年 | 37篇 |
2020年 | 13篇 |
2019年 | 26篇 |
2018年 | 35篇 |
2017年 | 29篇 |
2016年 | 53篇 |
2015年 | 90篇 |
2014年 | 140篇 |
2013年 | 166篇 |
2012年 | 203篇 |
2011年 | 194篇 |
2010年 | 126篇 |
2009年 | 123篇 |
2008年 | 156篇 |
2007年 | 168篇 |
2006年 | 182篇 |
2005年 | 174篇 |
2004年 | 167篇 |
2003年 | 143篇 |
2002年 | 166篇 |
2001年 | 32篇 |
2000年 | 32篇 |
1999年 | 53篇 |
1998年 | 61篇 |
1997年 | 47篇 |
1996年 | 45篇 |
1995年 | 41篇 |
1994年 | 33篇 |
1993年 | 36篇 |
1992年 | 47篇 |
1991年 | 41篇 |
1990年 | 40篇 |
1989年 | 32篇 |
1988年 | 37篇 |
1987年 | 17篇 |
1986年 | 16篇 |
1985年 | 30篇 |
1984年 | 34篇 |
1983年 | 21篇 |
1982年 | 33篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1972年 | 10篇 |
排序方式: 共有3334条查询结果,搜索用时 15 毫秒
91.
92.
The effects of lowering the pH on Photosystem II have been studied by measuring changes in absorbance and electron spin resonance in spinach chloroplasts.At pH values around 4 a light-induced dark-reversible chlorophyll oxidation by Photosystem II was observed. This chlorophyll is presumably the primary electron donor of system II. At pH values between 5 and 4 steady state illumination induced an ESR signal, similar in shape and amplitude to signal II, which was rapidly reversed in the dark. This may reflect the accumulation of the oxidized secondary donor upon inhibition of oxygen evolution. Near pH 4 the rapidly reversible signal and the stable and slowly decaying components of signal II disappeared irreversibly concomitant with the release of bound manganese.The results are discussed in relation to the effects of low pH on prompt and delayed fluorescence reported earlier (van Gorkom, H. J., Pulles, M. P. J., Haveman, J. and den Haan, G. A. (1976) Biochim. Biophys. Acta 423, 217–226). 相似文献
93.
Edwin M. Westbrook Paul B. Sigler Helen Berman Jenny P. Glusker Gerard Bunick Ann Benson Paul Talalay 《Journal of molecular biology》1976,103(3):665-667
A monoclinic crystal form (, β= 130.1 °) of Δ5-3-ketosteroid isomerase from Pseudomonas testosteroni (EC 5.3.3.1), grown at pH 7.0, has been characterized. Crystal-density measurements show that the asymmetric unit contains 12 protomers (Mr = 13,394). 相似文献
94.
Gerard A. Kennedy Grahame J. Coleman Stuart M. Armstrong 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1990,166(5):607-618
Summary The effects of restricted feeding schedules on the circadian rhythms of wheel-running of Dasyurus viverrinus were examined under a light/dark cycle and in constant darkness (experiment 1) and in constant light (experiment 2). The results of the 2 experiments showed that: (1) in contrast to the light/dark cycle, restricted feeding is only a weak zeitgeber for the wheel-running activity rhythms of D. viverrinus; (2) restricted feeding elicits meal anticipatory activity in D. viverrinus comparable to that elicited by restricted feeding in the rat; (3) transient cycles of the anticipatory activity free-run with a period different to that of the main component of activity for several cycles after the termination of restricted feeding; and (4) activity suggestive of beating between 2 oscillators occurs during restricted feeding and after the termination of restricted feeding. Taken together the latter 3 observations suggest that the activity rhythms of D. viverrinus are controlled by at least 2 separate circadian oscillators. 相似文献
95.
96.
97.
98.
99.
This study presents direct experimental evidence for assessing the electrostatic and non-electrostatic contributions of proteoglycans to the compressive equilibrium modulus of bovine articular cartilage. Immature and mature bovine cartilage samples were tested in unconfined compression and their depth-dependent equilibrium compressive modulus was determined using strain measurements with digital image correlation analysis. The electrostatic contribution was assessed by testing samples in isotonic and hypertonic saline; the combined contribution was assessed by testing untreated and proteoglycan-depleted samples.Though it is well recognized that proteoglycans contribute significantly to the compressive stiffness of cartilage, results demonstrate that the combined electrostatic and non-electrostatic contributions may add up to more than 98% of the modulus, a magnitude not previously appreciated. Of this contribution, about two thirds arises from electrostatic effects. The compressive modulus of the proteoglycan-depleted cartilage matrix may be as low as 3 kPa, representing less than 2% of the normal tissue modulus; experimental evidence also confirms that the collagen matrix in digested cartilage may buckle under compressive strains, resulting in crimping patterns. Thus, it is reasonable to model the collagen as a fibrillar matrix that can sustain only tension. This study also demonstrates that residual stresses in cartilage do not arise exclusively from proteoglycans, since cartilage remains curled relative to its in situ geometry even after proteoglycan depletion. These increased insights on the structure–function relationships of cartilage can lead to improved constitutive models and a better understanding of the response of cartilage to physiological loading conditions. 相似文献
100.
Nikhil N. Kulkarni Alan M. ONeill Tatsuya Dokoshi Elizabeth W.C. Luo Gerard C.L. Wong Richard L. Gallo 《The Journal of biological chemistry》2021,297(1)
Cathelicidins such as the human 37-amino acid peptide (LL-37) are peptides that not only potently kill microbes but also trigger inflammation by enabling immune recognition of endogenous nucleic acids. Here, a detailed structure–function analysis of LL-37 was performed to understand the details of this process. Alanine scanning of 34-amino acid peptide (LL-34) showed that some variants displayed increased antimicrobial activity against Staphylococcus aureus and group A Streptococcus. In contrast, different substitutions clustered on the hydrophobic face of the LL-34 alpha helix inhibited the ability of those variants to promote type 1 interferon expression in response to U1 RNA or to present U1 to the scavenger receptor (SR) B1 on the keratinocyte cell surface. Small-angle X-ray scattering experiments of the LL-34 variants LL-34, F5A, I24A, and L31A demonstrated that these peptides form cognate supramolecular structures with U1 characterized by inter-dsRNA spacings of approximately 3.5 nm, a range that has been previously shown to activate toll-like receptor 3 by the parent peptide LL-37. Therefore, while alanine substitutions on the hydrophobic face of LL-34 led to loss of binding to SRs and the complete loss of autoinflammatory responses in epithelial and endothelial cells, they did not inhibit the ability to organize with U1 RNA in solution to associate with toll-like receptor 3. These observations advance our understanding of how cathelicidin mediates the process of innate immune self-recognition to enable inert nucleic acids to trigger inflammation. We introduce the term “innate immune vetting” to describe the capacity of peptides such as LL-37 to enable certain nucleic acids to become an inflammatory stimulus through SR binding prior to cell internalization. 相似文献