全文获取类型
收费全文 | 6578篇 |
免费 | 531篇 |
国内免费 | 504篇 |
出版年
2023年 | 87篇 |
2022年 | 93篇 |
2021年 | 127篇 |
2020年 | 157篇 |
2019年 | 228篇 |
2018年 | 231篇 |
2017年 | 194篇 |
2016年 | 176篇 |
2015年 | 232篇 |
2014年 | 317篇 |
2013年 | 471篇 |
2012年 | 229篇 |
2011年 | 307篇 |
2010年 | 242篇 |
2009年 | 288篇 |
2008年 | 268篇 |
2007年 | 275篇 |
2006年 | 257篇 |
2005年 | 250篇 |
2004年 | 214篇 |
2003年 | 190篇 |
2002年 | 180篇 |
2001年 | 168篇 |
2000年 | 174篇 |
1999年 | 154篇 |
1998年 | 158篇 |
1997年 | 130篇 |
1996年 | 123篇 |
1995年 | 128篇 |
1994年 | 118篇 |
1993年 | 117篇 |
1992年 | 105篇 |
1991年 | 96篇 |
1990年 | 105篇 |
1989年 | 77篇 |
1988年 | 96篇 |
1987年 | 82篇 |
1986年 | 64篇 |
1985年 | 97篇 |
1984年 | 103篇 |
1983年 | 75篇 |
1982年 | 73篇 |
1981年 | 67篇 |
1980年 | 48篇 |
1979年 | 35篇 |
1978年 | 35篇 |
1977年 | 38篇 |
1975年 | 27篇 |
1974年 | 27篇 |
1973年 | 30篇 |
排序方式: 共有7613条查询结果,搜索用时 156 毫秒
991.
《Current biology : CB》2020,30(18):3657-3663.e5
Media player
992.
A. Ugolini B. Tiribilli C. Castellini 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,182(1):43-50
Experiments on compass orientation under artificial light were conducted with adult individuals of Talitrus saltator. The aim was to reproduce in the laboratory an orientation based on the sun compass corresponding to that recorded in conditions
of the true sun and sky. This was obtained by the creation within an opaque Plexiglas dome of a scenario that permitted variation
of the brightness of the artificial sky and sun. The results show that it is possible to obtain sun compass orientation corresponding
to the natural situation even in an artificial environment. It can be concluded that sandhoppers identify an artificial light
source as the sun if the artificial sky is also illuminated and if the intensities of the artificial sun and sky exceed certain
threshold values (1.13 and 10 μW cm−2, respectively). The results of other experiments under the natural blue sky with an artificial sun and with the real sun
attenuated are discussed.
Accepted: 23 May 1997 相似文献
993.
《Journal of molecular recognition : JMR》2017,30(6)
The interaction of a recently certified kinase inhibitor Tofacitinib (TFB) with bovine serum albumin (BSA) has been studied, by spectroscopic and molecular docking studies. Spectrofluorimetric measurements at 3 different temperatures (288, 298, and 310 K) showed that TFB quench the intrinsic fluorescence of BSA upon forming a nonfluorescent complex. The intrinsic fluorescence data showed that TFB binds to BSA with binding constant (K b) of approximately 104M−1, affirming a significant affinity of TFB with BSA. The decrease in Stern‐Volmer quenching constant with increasing temperature exhibited the static mechanism of quenching. Negative value of ΔG (−6.94 ± 0.32 kcal·mol−1), ΔH (−7.87 ± 0.52 kcal·mol−1), and ΔS (−3.14 ± 0.42 cal·mol−1·K−1) at all 3 temperatures declared the reaction between BSA and TFB to be spontaneous and exothermic. Far‐UV circular dichroism spectroscopy results demonstrated an increase in helical content of BSA in the presence of TFB. Moreover, dynamic light scattering measurements showed that TFB resulted into a decrease in the hydrodynamic radii (from 3.6 ± 0.053 to 2.9 ± 0.02 nm) of BSA. Molecular docking studies confirmed that TFB binds near site II on BSA, hydrogen bonding, and hydrophobic interaction were involved in the BSA‐TFB complex formation. The present study characterizing the BSA‐TFB interaction could be significant towards gaining an insight into the drug pharmacokinetics and pharmacodynamics and also in the direction of rational drug designing with better competence, against emerging immune‐mediated diseases, ie, alopecia and rheumatoid arthritis. 相似文献
994.
In bright sunlight photosynthetic activity is limited by the enzymatic machinery of carbon dioxide assimilation. This supererogation of energy can be easily visualized by the significant increases of photosynthetic activity under high CO2 conditions or other metabolic strategies which can increase the carbon flux from CO2 to metabolic pools. However, even under optimal CO2 conditions plants will provide much more NADPH + H+ and ATP that are required for the actual demand, yielding in a metabolic situation, in which no reducible NADP+ would be available. As a consequence, excited chlorophylls can activate oxygen to its singlet state or the photosynthetic electrons can be transferred to oxygen, producing highly active oxygen species such as the superoxide anion, hydroxyl radicals and hydrogen peroxide. All of them can initiate radical chain reactions which degrade proteins, pigments, lipids and nucleotides. Therefore, the plants have developed protection and repair mechanism to prevent photodamage and to maintain the physiological integrity of metabolic apparatus. The first protection wall is regulatory energy dissipation on the level of the photosynthetic primary reactions by the so-called non-photochemical quenching. This dissipative pathway is under the control of the proton gradient generated by the electron flow and the xanthophyll cycle. A second protection mechanism is the effective re-oxidation of the reduction equivalents by so-called “alternative electron cycling” which includes the water-water cycle, the photorespiration, the malate valve and the action of antioxidants. The third system of defence is the repair of damaged components. Therefore, plants do not suffer from energy shortage, but instead they have to invest in proteins and cellular components which protect the plants from potential damage by the supererogation of energy. Under this premise, our understanding and evaluation for certain energy dissipating processes such as non-photochemical quenching or photorespiration appear in a quite new perspective, especially when discussing strategies to improve the solar energy conversion into plant biomass. 相似文献
995.
P. Nick 《Plant biology (Stuttgart, Germany)》1997,110(4):291-297
The crown roots in the coleoptilar node of maize emerge asymmetrically: emergence at the dorsal flank of the node (opposite to the caryopsis) precedes emergence at the ventral flank (facing the caryopsis). This asymmetry can be altered by phototropic stimulation: emergence of crown roots is delayed in the lighted flank and promoted in the shaded flank causing an inversion of the endogenous asymmetry. The curvature induced by the phototropic stimulation is transient, the effect on crown root emergence, in contrast, persists. This stable effect is not a consequence of curvature per se and becomes irreversibly fixed between one and two hours after stimulation. The emergence of crown roots depends on directional signalling from the coleoptile to the node. The data are discussed in terms of a stable blue light induced transverse polarity of the coleoptile that can imprint a stable asymmetry upon the coleoptilar node guiding the emergence of crown roots. 相似文献
996.
《Journal of molecular biology》2022,434(23):167872
EF-hand Ca2+-binding proteins (CBPs), such as S100 proteins (S100s) and calmodulin (CaM), are signaling proteins that undergo conformational changes upon increasing intracellular Ca2+. Upon binding Ca2+, S100 proteins and CaM interact with protein targets and induce important biological responses. The Ca2+-binding affinity of CaM and most S100s in the absence of target is weak (CaKD > 1 μM). However, upon effector protein binding, the Ca2+ affinity of these proteins increases via heterotropic allostery (CaKD < 1 μM). Because of the high number and micromolar concentrations of EF-hand CBPs in a cell, at any given time, allostery is required physiologically, allowing for (i) proper Ca2+ homeostasis and (ii) strict maintenance of Ca2+-signaling within a narrow dynamic range of free Ca2+ ion concentrations, [Ca2+]free. In this review, mechanisms of allostery are coalesced into an empirical “binding and functional folding (BFF)” physiological framework. At the molecular level, folding (F), binding and folding (BF), and BFF events include all atoms in the biomolecular complex under study. The BFF framework is introduced with two straightforward BFF types for proteins (type 1, concerted; type 2, stepwise) and considers how homologous and nonhomologous amino acid residues of CBPs and their effector protein(s) evolved to provide allosteric tightening of Ca2+ and simultaneously determine how specific and relatively promiscuous CBP-target complexes form as both are needed for proper cellular function. 相似文献
997.
998.
《Current biology : CB》2021,31(24):5622-5632.e7
999.
Light environment change induces differential expression of guppy opsins in a multi‐generational evolution experiment
下载免费PDF全文
![点击此处可从《Evolution; international journal of organic evolution》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Alexandrea M. Kranz Leonard G. Forgan Gemma L. Cole John A. Endler 《Evolution; international journal of organic evolution》2018,72(8):1656-1676
Light environments critically impact species that rely on vision to survive and reproduce. Animal visual systems must accommodate changes in light that occur from minutes to years, yet the mechanistic basis of their response to spectral (color) changes is largely unknown. Here, we used a laboratory experiment where replicate guppy populations were kept under three different light environments for up to 8–12 generations to explore possible differences in the expression levels of nine guppy opsin genes. Previous evidence for opsin expression‐light environment “tuning” has been either correlative or focused exclusively on the relationship between the light environment and opsin expression over one or two generations. In our multigeneration experiment, the relative expression levels of nine different guppy opsin genes responded differently to light environment changes: some did not respond, while others differed due to phenotypic plasticity. Moreover, for the LWS‐1 opsin we found that, while we observed a wide range of plastic responses under different light conditions, common plastic responses (where the population replicates all followed the same trajectory) occurred only after multigenerational exposure to different light environments. Taken together this suggests that opsin expression plasticity plays an important role in light environment “tuning” in different light environments on different time scales, and, in turn, has important implications for both visual system function and evolution. 相似文献
1000.