全文获取类型
收费全文 | 8037篇 |
免费 | 457篇 |
国内免费 | 22篇 |
专业分类
8516篇 |
出版年
2024年 | 15篇 |
2023年 | 107篇 |
2022年 | 272篇 |
2021年 | 411篇 |
2020年 | 360篇 |
2019年 | 509篇 |
2018年 | 433篇 |
2017年 | 301篇 |
2016年 | 401篇 |
2015年 | 442篇 |
2014年 | 542篇 |
2013年 | 661篇 |
2012年 | 625篇 |
2011年 | 601篇 |
2010年 | 329篇 |
2009年 | 292篇 |
2008年 | 336篇 |
2007年 | 343篇 |
2006年 | 287篇 |
2005年 | 240篇 |
2004年 | 202篇 |
2003年 | 145篇 |
2002年 | 125篇 |
2001年 | 39篇 |
2000年 | 46篇 |
1999年 | 36篇 |
1998年 | 25篇 |
1997年 | 22篇 |
1996年 | 24篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 19篇 |
1992年 | 22篇 |
1991年 | 29篇 |
1990年 | 21篇 |
1989年 | 28篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 22篇 |
1985年 | 20篇 |
1984年 | 25篇 |
1983年 | 14篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1977年 | 5篇 |
1975年 | 7篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1972年 | 4篇 |
排序方式: 共有8516条查询结果,搜索用时 15 毫秒
41.
Sea snake (Microcephalophis gracilis) hemoglobin: Primary structure and relationships to other forms
The hemoglobin of the sea snakeMicrocephalophis gracilis was purified and the primary structure of the α and β chains determined. This is the first sea snake hemoglobin structure characterized, and apparently also the first complete structure of any snake hemoglobin (an α chain of a viper was known), allowing judgments of reptilian variants. Variations between the sea snake form and other reptilian forms are large (52–65 differences for the α chains), of similar order as those between the sea snake and avian (56–65 differences) or human (58 differences) forms. Functionally, 19 residues at α/β contact areas and 7 at heme contacts are exchanged in relation to the human α and β chains. Four positions of the sea snake hemoglobin contain residues thus far unique to this form. However, all replacements appear compatible with conserved overall functional properties. 相似文献
42.
Sulabha S. Keskar Sushama M. Gaikwad M.Islam Khan 《Enzyme and microbial technology》1996,18(8):602-604
Microbial α-mannosidases are used in the analysis of glycopeptides and the developmental regulation of lysosomal enzymes. This survey presents comparison of properties of this high molecular weight, oligomeric protein from a number of microbial sources. 相似文献
43.
Drought is an important environmental factor that can affect rhizobial competition and N2 fixation. Three alfalfa (Medicago sativa L. and M. falcata L.) accessions were grown in pots containing soil from an irrigated (Soil 1) and a dryland (Soil 2) alfalfa field in northern
Utah, USA. Mutants of three strains of Rhizobium meliloti Dang. from Pakistan (UL 136, UL 210, and UL 222) and a commercial rhizobial strain 102F51a were developed with various levels
of resistance to streptomycin. Seeds inoculated with these individual streptomycin-resistant mutants were sown in the two
soils containing naturalized rhizobial populations. Soils in the pots were maintained at −0.03, −0.5, and −1.0 MPa. After
10 weeks, plants were harvested and nodule isolates were cultured on agar medium with and without streptomycin to determine
nodule occupancy (proportion of the nodules occupied by introduced rhizobial strains). Number of nodules, nodule occupancy,
total plant dry weight, and shoot N were higher for Soil 1 than Soil 2. Number of nodules, plant dry weight, and shoot N decreased
as drought increased from −0.03 to −1.0 MPa in the three alfalfa accessions. Rhizobial strains UL 136 and UL 222 were competitive
with naturalized alfalfa rhizobia and were effective at symbiotic N2 fixation under drought. These results suggest that nodulation, growth, and N2 fixation in alfalfa can be improved by inoculation with competitive and drought-tolerant rhizobia and may be one economically
feasible way to increase alfalfa production in water-limited environments.
Joint contribution from USDA-ARS and the Utah Agric. Exp. Sta., Utah State Univ., Logan, UT 84322-4810, USA. Journal Paper
No. 4931.
Joint contribution from USDA-ARS and the Utah Agric. Exp. Sta., Utah State Univ., Logan, UT 84322-4810, USA. Journal Paper
No. 4931. 相似文献
44.
Molecular analysis of patients with beta-glucuronidase deficiency presenting as hydrops fetalis or as early mucopolysaccharidosis VII. 总被引:2,自引:0,他引:2 下载免费PDF全文
45.
Globoid cell leukodystrophy, or Krabbe disease, is a severe, autosomal recessive disorder resulting from a deficiency of galactocerebrosidase (GALC) activity. GALC is responsible for the lysosomal catabolism of certain galactolipids, including galactosylceramide and psychosine. In addition to the human patients, there are several naturally occurring animal models for this disease, including the twitcher mouse, West Highland White terriers (WHWT), and Cairn terriers. All species have deficient GALC activity and have the characteristic pathological findings in the nervous system. We now describe the cloning of the canine GALC cDNA and the identification of the disease-causing mutation in both terrier breeds. The 2007-bp open reading frame is 88% identical to that in human, and the deduced amino acid sequence is about 90% identical. However, the 3′-untranslated region is about 1 kb shorter than that in the human. Two nucleotide changes were found in affected dogs, an A to C transversion at cDNA position 473 (Y158S) and a C to T transition at position 1915 (P639S). Expression studies in COS-1 cells demonstrated that the A to C change at 473 is the disease-causing mutation. A rapid test for the identification of the genotype at that position has been developed, and over 100 WHWT and Cairn terriers have been screened. This will allow breeders to mate their dogs selectively and will permit the establishment of a colony of dogs for use in therapy trials. 相似文献
46.
N. Islam E. J. Evans 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1994,88(5):530-534
The effects of lodging and nitrogen rate were studied in a field trial of oilseed rapeBrassica napus L. Lodging decreased seed yield (16%) compared with a frame-raised crop. Yield decreased because of a significant reduction in each of the yield components coupled with a reduced plant population caused by stem breakage at the ground level. Lodging also reduced the final crop dry weight and harvest index. Seed yield was also lower when 200 kg ha–1 nitrogen was applied than with 400 kg ha–1. A general decrease in pod number m–2, seed nuber pod–1 and seed weight caused the lower yields. The use of 400 kg ha–1 of nitrogen changed the contribution of the terminal raceme and individual branches with respect to seed yield. Seed nitrogn content and nitrogen yield increased at the 400 kg ha–1, lowering both seed oil content and oil yield. 相似文献
47.
Mohammad B. Rashid Katsuhiko Shirahige Naotake Ogasawara Hiroshi Yoshikawa 《Gene》1994,150(2):213-220
We have analyzed the relationship between autonomously replicating sequence (ARS) structure and function for three ARS (ARS605, ARS607 and ARS609) from chromosome VI of Saccharomyces cerevisiae by systematic XhoI-linker mutation in the ARS consensus sequence (ACS) and flanking sequences. All mutations that encroached upon the ACS destroyed ARS activity. DNA sequences stimulative for ARS function were identified on either side of the ACS of ARS605 and only on the 3'-side of the ACS of ARS607. In ARS609, however, no such stimulative sequences were observed. Base substitutions complementary to the wild-type sequence of those stimulative regions, in ARS605 and ARS607, that did not change the AG of unwinding nor affected ARS activity suggests that these regions have, at least, a function as DNA-unwinding elements (DUE). ARS605, ARS607 and ARS609 DNA are of low AG value and showed hypersensitivity to single-strand-specific nuclease when inserted in negatively supercoiled plasmid. Linker mutations inhibitory for ARS activity (5L11 and 7L14) also caused significant changes in local nucleotide (nt) sensitivity within the ACS and its adjoining regions. Complementary base substitutions, however, did not affect these changes in local nt sensitivity. These results imply that the stimulative regions flanking the ACS are necessary to produce an optimum conformation around the ACS which may be important for full ARS activity. 相似文献
48.
M. Hossain M. R. Karim R. Islam O. I. Joarder 《Plant Cell, Tissue and Organ Culture》1993,34(2):199-203
A protocol for organogenesis from nucellar explants excised from fertilized ovules of immature fruits of Aegle marmelos Corr. was developed. Adventitious buds were initiated on Murashige and Skoog's (MS) medium containing various combinations of 6-benzyladenine (BA), -naphthalene-acetic acid (NAA), 3-indoleacetic acid and gibberellic acid. Medium containing 4.4 m BA and 2.7 M NAA produced the maximum number of adventitious buds per explant. Shoots were elongated by transferring explants with shoot buds to medium with a low concentration of BA (0.44 M). Rooting of in vitro-regenerated shoots was obtained in half-strength MS medium with 4.9 M indole-3-butyric acid. This is the first report of plant regeneration from nucellar explants of A. marmelos.Abbreviations BA
benzyladenine
- IAA
indoleacetic acid
- IBA
indolebutyric acid
- NAA
naphthaleneacetic acid
- GA3
gibberellic acid 相似文献
49.
50.