全文获取类型
收费全文 | 2191篇 |
免费 | 87篇 |
国内免费 | 3篇 |
专业分类
2281篇 |
出版年
2023年 | 24篇 |
2022年 | 53篇 |
2021年 | 85篇 |
2020年 | 63篇 |
2019年 | 57篇 |
2018年 | 82篇 |
2017年 | 64篇 |
2016年 | 108篇 |
2015年 | 117篇 |
2014年 | 139篇 |
2013年 | 168篇 |
2012年 | 224篇 |
2011年 | 180篇 |
2010年 | 118篇 |
2009年 | 92篇 |
2008年 | 85篇 |
2007年 | 75篇 |
2006年 | 58篇 |
2005年 | 62篇 |
2004年 | 50篇 |
2003年 | 52篇 |
2002年 | 50篇 |
2001年 | 27篇 |
2000年 | 25篇 |
1999年 | 17篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1971年 | 5篇 |
排序方式: 共有2281条查询结果,搜索用时 15 毫秒
1.
For estimation of growth, the efficiency of linked cross sectional scheme has been compared with pure longitudinal and cross sectional schemes. The relevant estimation theory has been developed and the expressions for the optimum estimators alongwith their variances have been derived. It has been observed that for estimation of growth, the linked cross-sectional scheme has been observed to be less efficient as compared to pure longitudinal scheme but more efficient than pure cross-sectional scheme. 相似文献
2.
O. P. Yadav V. K. Manga G. K. Gupta 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1993,87(5):558-560
Large-scale cultivation of pearl millet [Pennisetum glaucum (L.) R. Br. F1 hybrids in India has led to increased incidence of downy-mildew (Sclerospora graminicola). There is concern that the A1 male-sterile cytoplasm used in all the hybrids released so far is responsible for this increase. The influence of A1 malesterile cytoplasm on downy-mildew incidence in pearl millet was studied by comparing the disease reaction of 40 pairs of F1 hybrids, each pair carrying respectively a1 male-sterile and normal B cytoplasm. Mean downy-mildew incidence was similar in the hybrids carrying either A1 male-sterile or B cytoplasm. The general combining ability of lines with and without A1 cytoplasm was found to be similar for downy-mildew incidence. These results indicated that in pearl millet A1 cytoplasm is not associated with increased downymildew incidence. The possible danger of using only one source of cytoplasm has been briefly discussed. 相似文献
3.
A novel flavone glycoside was isolated from the methanolic extract of Cynotis axillaris Schult. Various analysis and characterization techniques were used to determine its structure and properties. The compound exhibited a melting point range of 231–232 °C and had a molecular formula of C27H30O14. Several spectral characterization techniques were employed to establish the isolated compound's structure. These included UV-visible spectroscopy, FT-IR, LC-ESI-MS, and NMR spectroscopy. Based on these analyses, the structure of the isolated compound was determined to be 5,7,4’-trihydroxyflavone-8-α-L-rhamnopyranoside-4’-O-β-D-galactopyranosyl. This structure indicates that it is a flavone glycoside consisting of a flavone (5,7,4’-trihydroxyflavone) moiety attached to a sugar molecule (galactopyranosyl) at position 4’, which further bears a rhamnose group at position 8 of the flavone. In addition, to the structural characterization, the compound also demonstrated significant antibacterial efficacy against various bacterial pathogens, including Gram-positive bacteria such as Bacillus subtilis MTCC441 and Gram-negative bacteria such as Escherichia coli MTCC1098, Proteus vulgarize MTCC426, and Salmonella Typhimurium MTCC3224. The antimicrobial activity was evaluated by measuring the zone of inhibition in millimetres, which provides an indication of the compound's ability to inhibit bacterial growth. The study successfully identified and characterized a novel flavone glycoside from Cynotis axillaris Schult. and its antimicrobial activity. 相似文献
4.
Summary In a pot culture experiment on a sierozem sandy soil (pH 8.2) rates of added B at 3 ppm although decreased root yield significantly
but shoot and grain yield was unaffected even at 6 ppm added B, even though shoot B concentration was as high as 360 ppm and
Ca/B ratio as low as 11. At 6 ppm applied B, shoot yield was increased by 18.5 per cent, whereas grain yield was at par with
control. The results suggested that Ca/B ratio in barley straw was not a reliable index for determing the magnitude of B problem
in the soil. 相似文献
5.
Structure and function in galactosyltransferase. Sequence locations of alpha-lactalbumin binding site, thiol groups, and disulfide bond 总被引:4,自引:0,他引:4
The region(s) of bovine galactosyltransferase that interacts with the lactose synthase regulatory protein alpha-lactalbumin was investigated using trace 3H acetylation to probe the effects of alpha-lactalbumin on the reactivities of the individual amino groups of galactosyltransferase. In the presence of Mn2+, alpha-lactalbumin was found to reduce the reactivities of lysines 93 and 181 and to increase the reactivities of one or more of lysines 230, 237, and 241. The addition of N-acetylglucosamine (20 mM), which enhances complex formation between the two proteins, did not significantly alter the pattern of perturbation. These results indicate that the NH2-terminal region of the catalytic domain of galactosyltransferase, and possibly part of the proline-rich "stem" region, is affected by the association with alpha-lactalbumin and is therefore implicated in the binding of acceptor substrates. In a separate study only cysteines 176, 266, and 342 of galactosyltransferase were found to react with [3H]iodoacetic acid under denaturing conditions. From their lack of reactivity it is deduced that the remaining two cysteines, residues 134 and 247, are joined in a disulfide linkage. From these results and those of a previous study of UDP-galactose binding (Yadav, S., and Brew, K. (1990) J. Biol. Chem. 265, 14163-14169) it appears that the soluble form of galactosyltransferase is composed of two domains, the NH2-terminal 150 residues containing the Cys134-Cys247 disulfide bond, which functions in alpha-lactalbumin and acceptor binding, and the COOH-terminal region, which is involved in UDP-galactose binding. 相似文献
6.
Five commercial preparations of natural pesticides were tested for in vitro compatibility with muscardine fungi, Beauveria brongniartii and Metarhizium anisopliae. Neemark (azadirachtin) was found compatible with both the fungi. Phytoallexin, the natural fungicide, significantly inhibited the growth of both the fungi, while other natural pesticides showed moderate to severe inhibition. 相似文献
7.
Umesh C. Haldar Sanat K. Saha Ronald C. Beavis Nirmal K. Sinha 《Journal of Protein Chemistry》1996,15(2):177-184
Two trypsin inhibitors, LA-1 and LA-2, have been isolated from ridged gourd (Luffa acutangula Linn.) seeds and purified to homogeneity by gel filtration followed by ion-exchange chromatography. The isoelectric point is atpH 4.55 for LA-1 and atpH 5.85 for LA-2. The Stokes radius of each inhibitor is 11.4 å. The fluorescence emission spectrum of each inhibitor is similar to that of the free tyrosine. The biomolecular rate constant of acrylamide quenching is 1.0×109 M–1 sec–1 for LA-1 and 0.8 × 109 M–1 sec–1 for LA-2 and that of K2HPO4 quenching is 1.6×1011 M–1 sec–1 for LA-1 and 1.2×1011M–1 sec–1 for LA-2. Analysis of the circular dichroic spectra yields 40%-helix and 60%-turn for La-1 and 45%-helix and 55%-turn for LA-2. Inhibitors LA-1 and LA-2 consist of 28 and 29 amino acid residues, respectively. They lack threonine, alanine, valine, and tryptophan. Both inhibitors strongly inhibit trypsin by forming enzymeinhibitor complexes at a molar ratio of unity. A chemical modification study suggests the involvement of arginine of LA-1 and lysine of LA-2 in their reactive sites. The inhibitors are very similar in their amino acid sequences, and show sequence homology with other squash family inhibitors. 相似文献
8.
Antonio Cabrera Umesh R. Rosyara Paolo De Franceschi Audrey Sebolt Suneth S. Sooriyapathirana Elisabeth Dirlewanger Jose Quero-Garcia Mirko Schuster Amy F. Iezzoni Esther van der Knaap 《Tree Genetics & Genomes》2012,8(2):237-247
The Rosaceae Conserved Orthologous Set (RosCOS) provides a gene-based genome-wide set of markers that have been used in comparative
analyses of peach (Prunus persica), apple (Malus × domestica), and strawberry (Fragaria spp.). In order to extend the use of these RosCOS to sweet cherry (Prunus avium L.), we identified markers that are polymorphic in breeding germplasm. Ninety-five percent (595/627) of previously designed
RosCOS primer pairs amplified a product in six sweet cherry cultivars predicted to represent the range of genetic diversity
in breeding germplasm. A total of 45% (282/627) RosCOS were polymorphic among the six cultivars, and allele number ranged
from 2 to 6, with a genome-wide mean of 2.35. A subset of 92 genome-wide single nucleotide polymorphisms (SNPs) corresponding
to 76 RosCOS was analyzed in 36 founder accessions and progeny. The expected and observed heterozygosity suggested that 83%
of the RosCOS were in Hardy–Weinberg equilibrium, implying that most RosCOS behave as neutral markers. Principal coordinate
analysis (PCO) identified one wild accession and two Spanish landraces that clustered differently from the other accessions.
The relatively high number of unique alleles found in the three differentially clustered selections suggested that their use
as parents has potential to increase the genetic diversity in future US-bred cultivars. Of the 92 RosCOS SNPs, 81 SNPs that
represented 68 genome-wide RosCOS segregated in four mapping populations. These RosCOS were mapped in four F1 populations, thereby greatly improving the genetic linkage map of sweet cherry. 相似文献
9.
Singh Awtar Bali Aradhana Kumar Ashwani Yadav Rajender Kumar Minhas Paramjit Singh 《Journal of Plant Growth Regulation》2022,41(5):1989-1998
Journal of Plant Growth Regulation - Exogenous applications of plant growth regulators (PGRs) were evaluated for their effects on growth, physiological attributes, and yield of sodicity stressed... 相似文献
10.
Pramod Kumar Yadav Peter Xie Ruma Banerjee 《The Journal of biological chemistry》2012,287(45):37611-37620
Human cystathionine β-synthase (CBS) is a unique pyridoxal 5′-phosphate (PLP)-dependent enzyme that has a regulatory heme cofactor. Previous studies have demonstrated the importance of Arg-266, a residue at the heme pocket end of α-helix 8, for communication between the heme and PLP sites. In this study, we have examined the role of the conserved Thr-257 and Thr-260 residues, located at the other end of α-helix 8 on the heme electronic environment and on activity. The mutations at the two positions destabilize PLP binding, leading to lower PLP content and ∼2- to ∼500-fold lower activity compared with the wild-type enzyme. Activity is unresponsive to PLP supplementation, consistent with the pyridoxine-nonresponsive phenotype of the T257M mutation in a homocystinuric patient. The H2S-producing activities, also impacted by the mutations, show a different pattern of inhibition compared with the canonical transsulfuration reaction. Interestingly, the mutants exhibit contrasting sensitivities to the allosteric effector, S-adenosylmethionine (AdoMet); whereas T257M and T257I are inhibited, the other mutants are hyperactivated by AdoMet. All mutants showed an increased propensity of the ferrous heme to form an inactive species with a 424 nm Soret peak and exhibited significantly reduced enzyme activity in the ferrous and ferrous-CO states. Our results provide the first evidence for bidirectional transmission of information between the cofactor binding sites, suggest the additional involvement of this region in allosteric communication with the regulatory AdoMet-binding domain, and reveal the potential for independent modulation of the canonical transsulfuration versus H2S-generating reactions catalyzed by CBS. 相似文献