全文获取类型
收费全文 | 3410篇 |
免费 | 132篇 |
国内免费 | 2篇 |
专业分类
3544篇 |
出版年
2023年 | 8篇 |
2022年 | 25篇 |
2021年 | 45篇 |
2020年 | 28篇 |
2019年 | 39篇 |
2018年 | 61篇 |
2017年 | 53篇 |
2016年 | 57篇 |
2015年 | 129篇 |
2014年 | 138篇 |
2013年 | 241篇 |
2012年 | 215篇 |
2011年 | 261篇 |
2010年 | 124篇 |
2009年 | 139篇 |
2008年 | 222篇 |
2007年 | 210篇 |
2006年 | 181篇 |
2005年 | 197篇 |
2004年 | 205篇 |
2003年 | 172篇 |
2002年 | 160篇 |
2001年 | 35篇 |
2000年 | 36篇 |
1999年 | 42篇 |
1998年 | 53篇 |
1997年 | 41篇 |
1996年 | 30篇 |
1995年 | 29篇 |
1994年 | 27篇 |
1993年 | 23篇 |
1992年 | 38篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 32篇 |
1988年 | 11篇 |
1987年 | 27篇 |
1986年 | 15篇 |
1985年 | 17篇 |
1984年 | 23篇 |
1983年 | 17篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 10篇 |
1973年 | 7篇 |
1971年 | 4篇 |
1970年 | 6篇 |
排序方式: 共有3544条查询结果,搜索用时 15 毫秒
41.
Thomas Lei Naoko Yamashita Takuya Watanabe Takayuki Kawahara Tomiyasu Miyaura 《Physiologia plantarum》2020,168(1):77-87
Daphne pseudomezereum A. Gray (Dpm) appears to be the only woody species in the north temperate forest that sheds its leaves in the summer while remaining green over winter (i.e. wintergreen leaf habit). Yet, the reason for this odd leaf habit has not been explored. To this end, we examined the microclimatic settings and ecophysiological traits of Dpm and its three native congeners in a field study of eight natural populations. In addition, we conducted a common garden experiment using Dpm plants where potential carbon gain across the seasons was estimated, using actual field microclimate data. Together, these data tested the hypothesis that Dpm retained traits of an open-grown upland ancestor, unable to adapt to the deep summer shade, it survived by becoming summer dormant and wintergreen. Our hypothesis was supported by patterns of leaf ecophysiological traits and carbon gain simulations in Dpm, consistent with the energetic feasibility of a summer dormancy followed by an autumn leaf sprout. We also conclude that carbon deficit driven by low light and high respiration cost is the trigger for the leaf habit of Dpm and assert that its phenological strategy represents a rare but viable alternative strategy for persistence in the temperate understory. 相似文献
42.
Satoshi Komoto Saori Fukuda Takayuki Murata Koki Taniguchi 《Microbiology and immunology》2020,64(6):401-406
A reverse genetics technology is an incredibly useful technique both for a proper understanding of different aspects of virus biology and for the generation of complementary DNA (cDNA)-derived infectious viruses, which can act as safe and effective vaccines and viral vectors. Rotaviruses (RVAs), especially human RVAs (HuRVAs), had been very refractory to this technology until very recently. Here, we describe the historical background of the development of a long-awaited HuRVA reverse genetics system, culminating in the generation of replicative HuRVAs entirely from cloned cDNAs. 相似文献
43.
There are two contradictory aspects of the adaptive process in evolution. The first is that species must optimally increase their own fitness in a given environment. The second is that species must maintain their variation to be ready to respond to changing environments. In a strict sense, these two aspects might consider to be mutually exclusive. If species are optimally adapted, then the variation in the species that is suboptimal decreases and vice versa. To resolve this dilemma, species must find a balance between optimal adaptation and robust adaptation. Finding the balance between these processes requires both the local and global complete, static information. However, the balance between the processes must be dynamic. In this study, we propose a model that illustrates dynamic negotiation between the global and local information using lattice theory. The dynamic negotiation between these two levels results in an overestimate of fitness for each species. The overestimation of fitness in our model represents the multiplicity of fitness which is sometimes discussed as the exaptation. We show that species in our model demonstrate the power law of the lifespan distribution and 1/f fluctuation for the adaptive process. Our model allows for a balance between optimal adaptation and robust adaptation without any arbitrary parameters. 相似文献
44.
In general, transferases undergo large structural changes and sequester substrate molecules, to shield them from water. By contrast, hydrolases exhibit only small structural changes, and expose substrate molecules to water. However, some hydrolases deeply bury their substrates within the proteins. To clarify the relationship between substrate‐shielding and enzymatic functions, we investigated 70 representative hydrolase structures, and examined the relative accessible surface areas of their substrates. As compared to the hydrolases employing the single displacement reaction, the hydrolases employing the double displacement reaction bury the substrate within the proteins. The exo hydrolases display significantly more substrate‐shielding from water than the endo hydrolases. It suggests that the substrate‐shielding is related to the chemical reaction mechanism of the hydrolases and the substrate specificity. Proteins 2013; © 2012 Wiley Periodicals, Inc. 相似文献
45.
Takayuki Shojima Rokusuke Yoshikawa Shigeki Hoshino Sayumi Shimode So Nakagawa Takuji Ohata Rie Nakaoka Takayuki Miyazawa 《Journal of virology》2013,87(17):9943-9948
We identified a new subgroup of koala retrovirus (KoRV), named KoRV-J, which utilizes thiamine transport protein 1 as a receptor instead of the Pit-1 receptor used by KoRV (KoRV-A). By subgroup-specific PCR, KoRV-J and KoRV-A were detected in 67.5 and 100% of koalas originating from koalas from northern Australia, respectively. Altogether, our results indicate that the invasion of the koala population by KoRV-J may have occurred more recently than invasion by KoRV-A. 相似文献
46.
Shoko Shinya Takayuki Ohnuma Reina Yamashiro Hisashi Kimoto Hideo Kusaoke Padmanabhan Anbazhagan André H. Juffer Tamo Fukamizo 《The Journal of biological chemistry》2013,288(42):30042-30053
Two carbohydrate binding modules (DD1 and DD2) belonging to CBM32 are located at the C terminus of a chitosanase from Paenibacillus sp. IK-5. We produced three proteins, DD1, DD2, and tandem DD1/DD2 (DD1+DD2), and characterized their binding ability. Transition temperature of thermal unfolding (Tm) of each protein was elevated by the addition of cello-, laminari-, chitin-, or chitosan-hexamer (GlcN)6. The Tm elevation (ΔTm) in DD1 was the highest (10.3 °C) upon the addition of (GlcN)6 and was markedly higher than that in DD2 (1.0 °C). A synergistic effect was observed (ΔTm = 13.6 °C), when (GlcN)6 was added to DD1+DD2. From isothermal titration calorimetry experiments, affinities to DD1 were not clearly dependent upon chain length of (GlcN)n; ΔGr° values were −7.8 (n = 6), −7.6 (n = 5), −7.6 (n = 4), −7.6 (n = 3), and −7.1 (n = 2) kcal/mol, and the value was not obtained for GlcN due to the lowest affinity. DD2 bound (GlcN)n with the lower affinities (ΔGr° = −5.0 (n = 3) ∼ −5.2 (n = 6) kcal/mol). Isothermal titration calorimetry profiles obtained for DD1+DD2 exhibited a better fit when the two-site model was used for analysis and provided greater affinities to (GlcN)6 for individual DD1 and DD2 sites (ΔGr° = −8.6 and −6.4 kcal/mol, respectively). From NMR titration experiments, (GlcN)n (n = 2∼6) were found to bind to loops extruded from the core β-sandwich of individual DD1 and DD2, and the interaction sites were similar to each other. Taken together, DD1+DD2 is specific to chitosan, and individual modules synergistically interact with at least two GlcN units, facilitating chitosan hydrolysis. 相似文献
47.
48.
Purified glycerol oxidase from Aspergillus japonicus AT 008 was homogeneous by ultracentrifugation and acrylamide gel electrophoresis. The molecular weight was determined to be 400,000 by sedimentation equilibrium, and the isoelectric point was found to be 4.9 by isoelectric focusing. The enzyme showed spectral characteristics of a heme protein. The reduced form possessed absorption maxima at 557 and 430 nm and the oxidized one at 557, 530, 420, 280, and 238 nm. The heme in the enzyme was identified as protoheme IX (one mol per mol of enzyme protein).Glycerol was the best substrate for the enzyme, and the Km value for glycerol was determined to be 10.4 mm. Dihydroxyacetone was oxidized at 59% of that for glycerol, but glycerol 3-phosphate, dihydroxyacetone phosphate, methanol, and ethanol were not oxidized at all. The enzyme had an optimal pH at 7.0 with glycerol as substrate, and the enzymatic activity increased by treatment in alkaline pH. The enzyme was also activated by addition of several divalent metal ions including Zn2+, Ni2+, and Mg2+. 相似文献
49.
Takayuki Oritani Sachio Kudo Kyohei Yamashita 《Bioscience, biotechnology, and biochemistry》2013,77(3):757-760
Asymmetric hydrolysis of acetate (10) of (±)-t-2,t-4-dimethyl-r-l-cyclohexanol with Bacillus subtilis var. niger gave (?)-(lS,2S,4S)-2,4-dimethyl-l-cyclohexanol (6a) and (+)-(1R,2R,4R)-acetate (10b) with high optical purities. Optically pure (?) and (+)-alcohols (6a and 6b) were prepared via corresponding 3,5-dinitrobenzoates. Oxidation of alcohols (6a and 6b) with chromic acid gave optically pure (?)-(2S,4S) and (+)-(2R,4R)-2,4-dimethyl-l-cyclohexanones (2a and 2b), respectively. 相似文献
50.
Photosensitized oxygenation of dehydro-β-ionylidene-ethanol afforded 1′-hydroxy-4′keto-α-ionylidene-ethanol, which was oxidized with active MnO2 to give 1′-hydroxy-4′-keto-α-ionylidene-acetaldehyde. The Wittig reaction of α-ionylideneacetaldehyde with carbethoxymethylenetriphenylphosphorane or the phosphorane prepared from ethyl γ-bromosenecioate gave ethyl α-ionylidene-crotonate or ethyl α-ionylidenesenecioate. Vitamin A2 acid ethyl ester was converted to the hydroxy-keto-ester by photosensitized oxygenation. About the above synthesized compounds were examined growth inhibitory activities on rice seedlings. 相似文献