全文获取类型
收费全文 | 7735篇 |
免费 | 548篇 |
国内免费 | 2篇 |
出版年
2023年 | 41篇 |
2022年 | 39篇 |
2021年 | 165篇 |
2020年 | 85篇 |
2019年 | 131篇 |
2018年 | 151篇 |
2017年 | 142篇 |
2016年 | 245篇 |
2015年 | 361篇 |
2014年 | 405篇 |
2013年 | 528篇 |
2012年 | 594篇 |
2011年 | 586篇 |
2010年 | 414篇 |
2009年 | 317篇 |
2008年 | 466篇 |
2007年 | 447篇 |
2006年 | 468篇 |
2005年 | 399篇 |
2004年 | 407篇 |
2003年 | 358篇 |
2002年 | 344篇 |
2001年 | 83篇 |
2000年 | 61篇 |
1999年 | 78篇 |
1998年 | 75篇 |
1997年 | 83篇 |
1996年 | 59篇 |
1995年 | 39篇 |
1994年 | 51篇 |
1993年 | 41篇 |
1992年 | 42篇 |
1991年 | 32篇 |
1990年 | 30篇 |
1989年 | 37篇 |
1988年 | 31篇 |
1987年 | 24篇 |
1986年 | 26篇 |
1985年 | 38篇 |
1984年 | 29篇 |
1983年 | 27篇 |
1982年 | 37篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 20篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1975年 | 13篇 |
1974年 | 14篇 |
1973年 | 27篇 |
排序方式: 共有8285条查询结果,搜索用时 31 毫秒
991.
992.
Changes in the texture and viscoelastic properties of bread containing rice porridge during storage 总被引:1,自引:0,他引:1
Tsai CL Sugiyama J Shibata M Kokawa M Fujita K Tsuta M Nabetani H Araki T 《Bioscience, biotechnology, and biochemistry》2012,76(2):331-335
The objective of this study was to investigate the effects of rice porridge on the texture and viscoelastic properties of bread during storage. Three types of bread, wheat flour bread, 15% rice flour bread, and 15% rice porridge bread, were prepared. After baking and storing the bread for 24 h, 48 h, and 72 h at room temperature, we measured the texture and viscoelastic properties of the bread crumbs by texture profile analysis (TPA) and creep test. The 15% rice porridge bread showed a significantly higher specific volume and maintained softer crumbs than the other two types (p<0.05). It also had a slightly stickier texture than the others. It can be concluded that rice porridge improves the specific volume, texture, and viscoelastic properties of bread crumbs during storage. 相似文献
993.
The results of the present investigation show the susceptibility of tyrosine to undergo visible light-induced photomodification
to 3-nitrotyrosine in the presence of nitrite and riboflavin, as sensitizer. By changing H2O by D2O, it could be established that singlet oxygen has a minor role in the reaction. The finding that nitration of tyrosine still
occurred to a large extent under anaerobic conditions indicates that the process proceeds mainly through a type I mechanism,
which involves the direct interaction of the excited state of riboflavin with tyrosine and nitrite to give tyrosyl radical
and nitrogen dioxide radical, respectively. The tyrosyl radicals can either dimerize to yield 3,3′-dityrosine or combine with
nitrogen dioxide radical to form 3-nitrotyrosine. The formation of 3-nitrotyrosine was found to increase with the concentration
of nitrite added and was accompanied by a decrease in the recovery of 3,3′-dityrosine, suggesting that tyrosine nitration
competes with dimerization reaction. The riboflavin photosensitizing reaction in the presence of nitrite was also able to
induce nitration of tyrosine residues in proteins as revealed by the spectral changes at 430 nm, a characteristic absorbance
of 3-nitrotyrosine, and by immunoreactivity using 3-nitrotyrosine antibodies. Since riboflavin and nitrite are both present
endogenously in living organism, it is suggested that this pathway of tyrosine nitration may potentially occur in tissues
and organs exposed to sunlight such as skin and eye. 相似文献
994.
Bottai D Di Luca M Majlessi L Frigui W Simeone R Sayes F Bitter W Brennan MJ Leclerc C Batoni G Campa M Brosch R Esin S 《Molecular microbiology》2012,83(6):1195-1209
The chromosome of Mycobacterium tuberculosis encodes five type VII secretion systems (ESX-1-ESX-5). While the role of the ESX-1 and ESX-3 systems in M. tuberculosis has been elucidated, predictions for the function of the ESX-5 system came from data obtained in Mycobacterium marinum, where it transports PPE and PE_PGRS proteins and modulates innate immune responses. To define the role of the ESX-5 system in M. tuberculosis, in this study, we have constructed five M. tuberculosis H37Rv ESX-5 knockout/deletion mutants, inactivating eccA(5), eccD(5), rv1794 and esxM genes or the ppe25-pe19 region. Whereas the Mtbrv1794ko displayed no obvious phenotype, the other four mutants showed defects in secretion of the ESX-5-encoded EsxN and PPE41, a representative member of the large PPE protein family. Strikingly, the MtbeccD(5) ko mutant also showed enhanced sensitivity to detergents and hydrophilic antibiotics. When the virulence of the five mutants was evaluated, the MtbeccD(5) ko and MtbΔppe25-pe19 mutants were found attenuated both in macrophages and in the severe combined immune-deficient mouse infection model. Altogether these findings indicate an essential role of ESX-5 for transport of PPE proteins, cell wall integrity and full virulence of M. tuberculosis, thereby opening interesting new perspectives for the study of this human pathogen. 相似文献
995.
Mario Kampa Wolfgang Lubitz Maurice van Gastel Frank Neese 《Journal of biological inorganic chemistry》2012,17(8):1269-1281
[NiFe] hydrogenases catalyze the reversible formation of H2. The [NiFe] heterobimetallic active site is rich in redox states. Here, we investigate the key catalytic state Ni?CC of Desulfovibrio vulgaris Miyazaki F hydrogenase using a cluster model that includes the truncated amino acids of the entire second coordination sphere of the enzyme. The optimized geometries, computed g?tensors, hyperfine coupling constants, and IR stretching frequencies all agree well with experimental values. For the hydride in the bridging position, only a single minimum on the potential energy surface is found, indicating that the hydride bridges and binds to both nickel and iron. The influence of the second coordination sphere on the electronic structure is investigated by comparing results from the large cluster models with truncated models. The largest interactions of the second coordination sphere with the active site concern the hydrogen bonds with the cyanide ligands, which modulate the bond between iron and these ligands. Secondly, the electronic structure of the active site is found to be sensitive to the protonation state of His88. This residue forms a hydrogen bond with the spin-carrying sulfur atom of Cys549, which in turn tunes the spin density at the nickel and coordinating sulfur atoms. In addition, the unequal distribution of spin density over the equatorial cysteine residues results from different orientations of the cysteine side chains, which are kept in their particular orientation by the secondary structure of the protein. 相似文献
996.
Yang SW Smotryski J McElroy WT Tan Z Ho G Tulshian D Greenlee WJ Guzzi M Zhang X Mullins D Xiao L Hruza A Chan TM Rindgen D Bleickardt C Hodgson R 《Bioorganic & medicinal chemistry letters》2012,22(1):235-239
A series of pyrazoloquinoline analogs have been synthesized and shown to bind to PDE10 with high affinity. From the SAR study and our lead optimization efforts, compounds 16 and 27 were found to possess potent oral antipsychotic activity in the MK-801 induced hyperactive rat model. 相似文献
997.
Christian Jebsen Alessandra Norici Heiko Wagner Matteo Palmucci Mario Giordano Christian Wilhelm 《Physiologia plantarum》2012,146(4):427-438
Fourier transform infrared (FTIR) spectra were measured from cells of Microcystis aeruginosa and Protoceratium reticulatum, whose growth rates were manipulated by the availability of nutrients or light. As expected, the macromolecular composition changed in response to the treatments. These changes were species‐specific and depended on the type of perturbation applied to the growth regime. Microcystis aeruginosa showed an increase in the carbohydrate‐to‐protein ratio with decreased growth rates, under nutrient limitation, whereas light limitation induced a decrease of the carbohydrate‐to‐protein ratio with decreasing proliferation rates. The macromolecular pools of P. reticulatum showed a higher degree of compositional homeostasis. Only when the lowest light irradiance and nutrient availability were supplied, an increase of the carbohydrate‐to‐protein FTIR absorbance ratio was observed. A species‐specific partial least squares (PLS) model was developed using the whole FTIR spectra. This model afforded a very high correlation between the predicted and the measured growth rates, regardless of the growth conditions. On the contrary, the prediction based on absorption band ratios generally used in FTIR studies would strongly depend on growth conditions. This new computational method could constitute a substantial improvement in the early warning systems of algal blooms and, in general, for the study of algal growth, e.g. in biotechnology. Furthermore, these results confirm the suitability of FTIR spectroscopy as a tool to map complex biological processes like growth under different environmental conditions. 相似文献
998.
999.
1000.
X Jiao DJ Kopecky J Liu J Liu JC Jaen MG Cardozo R Sharma N Walker H Wesche S Li E Farrelly SH Xiao Z Wang F Kayser 《Bioorganic & medicinal chemistry letters》2012,22(19):6212-6217
Two classes of ACK1 inhibitors, 4,5,6-trisubstituted furo[2,3-d]pyrimidin4-amines and 4,5,6-trisubstituted 7H-pyrrolo[2,3-d]pyrimidin-4-amines, were discovered and evaluated as ACK1 inhibitors. Further structural refinement led to the identification of potent and selective dithiolane inhibitor 37. 相似文献