全文获取类型
收费全文 | 8315篇 |
免费 | 788篇 |
国内免费 | 7篇 |
专业分类
9110篇 |
出版年
2022年 | 59篇 |
2021年 | 121篇 |
2020年 | 68篇 |
2019年 | 93篇 |
2018年 | 118篇 |
2017年 | 112篇 |
2016年 | 177篇 |
2015年 | 306篇 |
2014年 | 352篇 |
2013年 | 451篇 |
2012年 | 534篇 |
2011年 | 552篇 |
2010年 | 391篇 |
2009年 | 364篇 |
2008年 | 484篇 |
2007年 | 491篇 |
2006年 | 443篇 |
2005年 | 429篇 |
2004年 | 432篇 |
2003年 | 404篇 |
2002年 | 393篇 |
2001年 | 89篇 |
2000年 | 72篇 |
1999年 | 117篇 |
1998年 | 136篇 |
1997年 | 86篇 |
1996年 | 87篇 |
1995年 | 80篇 |
1994年 | 82篇 |
1993年 | 78篇 |
1992年 | 64篇 |
1991年 | 69篇 |
1990年 | 89篇 |
1989年 | 67篇 |
1988年 | 64篇 |
1987年 | 69篇 |
1986年 | 55篇 |
1985年 | 68篇 |
1984年 | 75篇 |
1983年 | 71篇 |
1982年 | 77篇 |
1981年 | 62篇 |
1980年 | 70篇 |
1979年 | 52篇 |
1978年 | 54篇 |
1977年 | 51篇 |
1976年 | 54篇 |
1974年 | 43篇 |
1973年 | 54篇 |
1971年 | 30篇 |
排序方式: 共有9110条查询结果,搜索用时 15 毫秒
991.
A modified method for determining protein binding capacity of plant polyphenolics using radiolabelled protein 总被引:1,自引:0,他引:1
Henson GL Niemeyer L Ansong G Forkner R Makkar HP Hagerman AE 《Phytochemical analysis : PCA》2004,15(3):159-163
A modified radiochemical protein binding method for determining the protein binding capacity of plant polyphenolics (tannins) is described. Purified tannin or unfractionated plant extracts were immobilised on filter paper discs and incubated with the 125I-labelled bovine serum albumin. Protein bound to the disc was proportional to the amount of tannin applied to the disc, although at high concentrations of polyphenolics the discs became saturated and the relationship was no longer applicable. The method was validated using purified procyanidin from Sorghum grain and has been applied to crude polyphenolic extracts from maple, white oak, black oak, walnut and tulip poplar leaves. Specific chemical assays for the determination of proanthocyanidins (acid butanol method) and hydrolysable tannins (modified potassium iodate method) were employed to validate the new protein binding method with the complex plant extracts. 相似文献
992.
Mary Anne Wenck Francisco J Medrano Ann E Eakin Sydney P Craig 《Biochimica et Biophysica Acta - Proteins and Proteomics》2004,1700(1):11-18
The kinetic mechanism for the reaction catalyzed by the hypoxanthine phosphoribosyltransferase (HPRT) from Trypanosoma cruzi was analyzed to determine the feasibility of designing a parasite-specific mechanism-based inhibitor of this enzyme. The results show that the HPRT from T. cruzi follows an essentially ordered bi–bi reaction, and like its human counterpart also likely forms a dead end complex with purine substrates and the product pyrophosphate. Computational fitting of the kinetics data to multiple initial velocity equations gave results that are consistent with the dead end complex arising when the hypoxanthine- or guanine-bound form of the enzyme binds pyrophosphate rather than the phosphoribosylpyrophosphate substrate of the productive forward reaction. Limited proteolytic digestion was employed to provide additional support for formation of the dead end complex and to estimate the Kd values for substrates of both the forward and reverse reactions. Due to similarities with the kinetic mechanism of the human HPRT, the results reported here for the HPRT from T. cruzi indicate that the design of a mechanism-based inhibitor of the trypanosomal HPRT, that would not also inhibit the human enzyme, may be difficult. However, the results also show that a potent selective inhibitor of the trypanosomal HPRT might be achieved via the design of a bi-substrate type inhibitor that incorporates analogs of moieties for a purine base and pyrophosphate. 相似文献
993.
994.
Karam El-Bayoumy Edmond J. Lavoie Stephen S. Hecht Elizabeth Ann Fow Dietrich Hoffmann 《Mutation research》1981,90(2):143-147
Mitogen-stimulated lymphocytes from 8 healthy donors were exposed to interferon, and cytogenetic studies were preformed. The response of lymphocytes to the mitogens phytohemagglutinin (PHA), concanavalin A (con A) and pokeweed mitogen (PWM) was inhibited by interferon, whereas an increased number of structural chromosomal aberrations was not detected. Further investigations of the cytogenetic effects of interferon are needed. 相似文献
995.
Bucklin Ann; Smolenack Sara B.; Bentley Alyssa M.; Wiebe Peter H. 《Journal of plankton research》1997,19(11):1763-1781
Population genetic structure and patterns of gene flow are describedfor the euphausiid, Meganyctiphanes norvegica, in the NW AtlanticOcean based on DNA sequence variation of two regions of mitochondrialDNA (mtDNA). DNA sequences were determined for portions of cytochromeoxidase I (COI; 400 base pairs; 76 individuals) and cytochromeb (CYB; 300 base pairs; 101 individuals) for euphausiids collectedfrom the Gulf of Maine in 1991, the Gulf of St Lawrence in 1993and 1994, the Scotian Shelf in 1994, and Georges Bank in 1994.For comparison, M.norvegica collected from the fjords of westernNorway in 1992 were sequenced for COI (20 individuals) and CYB(18 individuals). COI was less variable than CYB, based on bothhaplotype (h=0.6847 for COI; 0.9077 for CYB) and nucleotidediversities ( 相似文献
996.
Ming Li Wang Lu Huang Deverie K. Bongard-Pierce Stephen Belmonte Eve Ann Zachgo John W. Morris Maureen Dolan Howard M. Goodman 《The Plant journal : for cell and molecular biology》1997,12(3):711-730
A method for construction of bacterial artificial chromosome (BAC) contigs from a yeast artifical chromosome (YAC) physical map is described. An ∼2 Mb contig, consisting of two large BAC contigs linked by a small YAC, has been assembled in the region around 80 cM of Arabidopsis thaliana chromosome 2. Clones from this contig will facilitate gene isolation in the region and can be used directly as substrates for DNA sequencing. 相似文献
997.
998.
Dmitry Shevela Gennady Ananyev Ann K. Vatland Janine Arnold Fikret Mamedov Lutz A. Eichacker G. Charles Dismukes Johannes Messinger 《Physiologia plantarum》2019,166(1):165-180
High solar flux is known to diminish photosynthetic growth rates, reducing biomass productivity and lowering disease tolerance. Photosystem II (PSII) of plants is susceptible to photodamage (also known as photoinactivation) in strong light, resulting in severe loss of water oxidation capacity and destruction of the water‐oxidizing complex (WOC). The repair of damaged PSIIs comes at a high energy cost and requires de novo biosynthesis of damaged PSII subunits, reassembly of the WOC inorganic cofactors and membrane remodeling. Employing membrane‐inlet mass spectrometry and O2‐polarography under flashing light conditions, we demonstrate that newly synthesized PSII complexes are far more susceptible to photodamage than are mature PSII complexes. We examined these ‘PSII birth defects’ in barley seedlings and plastids (etiochloroplasts and chloroplasts) isolated at various times during de‐etiolation as chloroplast development begins and matures in synchronization with thylakoid membrane biogenesis and grana membrane formation. We show that the degree of PSII photodamage decreases simultaneously with biogenesis of the PSII turnover efficiency measured by O2‐polarography, and with grana membrane stacking, as determined by electron microscopy. Our data from fluorescence, QB‐inhibitor binding, and thermoluminescence studies indicate that the decline of the high‐light susceptibility of PSII to photodamage is coincident with appearance of electron transfer capability QA? → QB during de‐etiolation. This rate depends in turn on the downstream clearing of electrons upon buildup of the complete linear electron transfer chain and the formation of stacked grana membranes capable of longer‐range energy transfer. 相似文献
999.
Quantitative zooplankton samples were obtained monthly or bi-monthly 15 times from June 1974 to May 1975 at three stations in lower Delaware Bay. Two 12-hour cruises were also conducted at one of the stations.Arthropods dominated the samples in terms of number of species and number of individuals. The number of zooplankton from surface samples ranged from 58/m3 in August to 21,092/ m3 in June, while bottom samples varied from 259/m3 in August to 30,395/ m3 in October. In general, larger concentrations of individuals were found in bottom samples.Only on three occasions did meroplankton exceed the holoplankton, and these occurred at the shallow water stations. Meroplankton comprised a larger percentage of the bottom samples than surface samples. Zoeae of Neopanope sayi and Uca sp. contributed mainly to the large proportion of meroplankton in July 1974, veligers of Mytilus edulis in January 1975, and nauplii of Balanus sp. in May 1975.Copepods were the largest component of the population throughout most of the year. At all stations and depths, Arctica tonsa dominated most of the summer samples. In the spring of 1975, A. tonsa was replaced by Centropages hamatus, Temora longicornis, and Pseudocalanus minutus.During the 12-hour cruises there were higher numbers of individuals in the bottom waters in the day with migration to surface waters in the afternoon and evening. Based on cluster analysis, five time-related assemblages were discerned: June, July–August, September–November, December, January–May. Comparison of Delaware Bay zooplankton with other estuarine systems indicated that the densities obtained locally were most similar to those reported in the York River, Virginia. 相似文献
1000.
Sohee Baek Nam Joo Kang Grzegorz M. Popowicz Marcelino Arciniega Sung Keun Jung Sanguine Byun Nu Ry Song Yong-Seok Heo Bo Yeon Kim Hyong Joo Lee Tad A. Holak Martin Augustin Ann M. Bode Robert Huber Zigang Dong Ki Won Lee 《Journal of molecular biology》2013,425(2):411-423
c-Jun NH2-terminal kinases (JNKs) and phosphatidylinositol 3-kinase (PI3-K) play critical roles in chronic diseases such as cancer, type II diabetes, and obesity. We describe here the binding of quercetagetin (3,3′,4′,5,6,7-hydroxyflavone), related flavonoids, and SP600125 to JNK1 and PI3-K by ATP-competitive and immobilized metal ion affinity-based fluorescence polarization assays and measure the effect of quercetagetin on JNK1 and PI3-K activities. Quercetagetin attenuated the phosphorylation of c-Jun and AKT, suppressed AP-1 and NF-κB promoter activities, and also reduced cell transformation. It attenuated tumor incidence and reduced tumor volumes in a two-stage skin carcinogenesis mouse model.Our crystallographic structure determination data show that quercetagetin binds to the ATP-binding site of JNK1. Notably, the interaction between Lys55, Asp169, and Glu73 of JNK1 and the catechol moiety of quercetagetin reorients the N-terminal lobe of JNK1, thereby improving compatibility of the ligand with its binding site. The results of a theoretical docking study suggest a binding mode of PI3-K with the hydroxyl groups of the catechol moiety forming hydrogen bonds with the side chains of Asp964 and Asp841 in the p110γ catalytic subunit. These interactions could contribute to the high inhibitory activity of quercetagetin against PI3-K. Our study suggests the potential use of quercetagetin in the prevention or therapy of cancer and other chronic diseases. 相似文献