全文获取类型
收费全文 | 5177篇 |
免费 | 290篇 |
国内免费 | 318篇 |
专业分类
5785篇 |
出版年
2024年 | 23篇 |
2023年 | 75篇 |
2022年 | 76篇 |
2021年 | 123篇 |
2020年 | 131篇 |
2019年 | 131篇 |
2018年 | 158篇 |
2017年 | 105篇 |
2016年 | 133篇 |
2015年 | 133篇 |
2014年 | 289篇 |
2013年 | 358篇 |
2012年 | 243篇 |
2011年 | 349篇 |
2010年 | 254篇 |
2009年 | 324篇 |
2008年 | 355篇 |
2007年 | 353篇 |
2006年 | 281篇 |
2005年 | 268篇 |
2004年 | 233篇 |
2003年 | 218篇 |
2002年 | 181篇 |
2001年 | 137篇 |
2000年 | 119篇 |
1999年 | 103篇 |
1998年 | 101篇 |
1997年 | 47篇 |
1996年 | 46篇 |
1995年 | 55篇 |
1994年 | 40篇 |
1993年 | 43篇 |
1992年 | 40篇 |
1991年 | 28篇 |
1990年 | 27篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1985年 | 24篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1976年 | 7篇 |
1973年 | 4篇 |
1972年 | 5篇 |
排序方式: 共有5785条查询结果,搜索用时 0 毫秒
51.
S. H. Park R. T. Raines 《Protein science : a publication of the Protein Society》1997,6(11):2344-2349
Green fluorescent protein (GFP) is autofluorescent. This property has made GFP useful in monitoring in vivo activities such as gene expression and protein localization. We find that GFP can be used in vitro to reveal and characterize protein-protein interactions. The interaction between the S-peptide and S-protein fragments of ribonuclease A was chosen as a model system. GFP-tagged S-peptide was produced, and the interaction of this fusion protein with S-protein was analyzed by two distinct methods: fluorescence gel retardation and fluorescence polarization. The fluorescence gel retardation assay is a rapid method to demonstrate the existence of a protein-protein interaction and to estimate the dissociation constant (Kd) of the resulting complex. The fluorescence polarization assay is an accurate method to evaluate Kd in a specified homogeneous solution and can be adapted for the high-throughput screening of protein or peptide libraries. These two methods are powerful new tools to probe protein-protein interactions. 相似文献
52.
Proteolytic activity of proteasome on myofibrillar structures 总被引:5,自引:0,他引:5
Richard G. Taylor Caroline Tassy Mariele Briand Nathalie Robert Yves Briand Ahmed Ouali 《Molecular biology reports》1995,21(1):71-73
The physiologic function of proteasome remains unclear. Evidence suggests a role in degradation of ubiquitin-protein conjugates, MHC antigen presentation, and some specificity of substrate within certain cell types. To explore further the properties of proteasome we have examined its effect on a well defined structure, the myofibril. We find that despite its large size (20S) proteasome is able to degrade myofibrils and intact, permeabilized muscle fibrils. The proteins degraded showed some specificity because actin, myosin and desmin were degraded faster than -actinin, troponin T and tropomyosin. Changes in ultrastructure were slow and included a general loss of structure with Z and I bands effected before the M band and costameres. 相似文献
53.
Izaura Yoshico Hirata Maria Helena Sedenho Cezari Clovis Ryuichi Nakaie Paulo Boschcov Amando Siuiti Ito Maria Aparecida Juliano Luiz Juliano 《Letters in Peptide Science》1995,1(6):299-308
Summary A general procedure, using the commonly employed solid-phase peptide synthesis methodology for obtaining internally quenched fluorogenic peptides with ortho-aminobenzoyl/dinitrophenyl groups as donor-acceptor pairs, is presented. The essential feature of this procedure is the synthesis of an N
-Boc or-Fmoc derivative of glutamic acid with the -carboxyl group bound to N-(2,4-dinitrophenyl)-ethylenediamine (EDDnp), which provides the quencher moiety attached to the C-terminus of the substrate. The fluorescent donor group, ortho-aminobenzoic acid (Abz), is incorporated into the resin-bound peptide in the last coupling cycle. Depending on the resin type used, Abz-peptidyl-Gln-EDDnp or Abz-peptidyl-Glu-EDDnp is obtained. Using the procedure described above, substrates for human renin and tissue kallikreins were synthesised. Spectrofluorimetric measurements of Abz bound to the -amino group of proline showed that strong quenching of Abz fluorescence occurs in the absence of any acceptor group. 相似文献
54.
Staining of living bacteria with rhodamine 123 总被引:5,自引:0,他引:5
Tohey Matsuyama 《FEMS microbiology letters》1984,21(2):153-157
Abstract It is possible to stain live bacteria with rhodamine 123 (R123). The stained fluorescent cells still keep the ability to replicate ( Staphylococcus aureus, Bordetella pertussis ) and to swim (e.g., Salmonella minnesota ). Dead cells or cells with a dissipated transmembrane potential showed markedly diminished fluorescence. Gram-negative strains were stained with different efficiency, presumably reflecting the different constitutions of the outer membrane. 相似文献
55.
Stanley S. Stadnicki Franklin R. Leach 《In vitro cellular & developmental biology. Plant》1978,14(7):601-605
Summary HeLa and L-M cells can be effectively grown directly on glass fiber filters to yield replicate cultures that allow easy analysis
of biosynthetic capabilities through measurement of radioactive precursor uptake and incorporation. The glass fiber filters
are superior to glass cover slips, growth in scintillation vials, and growth on Millipore filters in the ease of handling
during experimental treatment and in the amount of radioactivity incorporated during the labeling period. These parameters
are experimentally established and a typical application of the procedure that demonstrates the hydroxyurea inhibition of
DNA synthesis is presented.
This research was supported by Oklahoma Agricultural Experiment Station Project 1534. This publication is Article J-3334 of
the Oklahoma Agricultural Experimental Station. 相似文献
56.
Summary The anterior end of the zoospore ofUlothrix belkae has been examined in detail and is compared toStigeoclonium and other filamentous green algae. The nature of the symmetry of green algal motile cells is discussed and the term, 180° rotational symmetry, is proposed to describe the type of arrangement of anterior end components seen inU. belkae, including the four basal bodies, rootlets and striated fibers. The four microtubular rootlets are cruciately arranged. A striated microtubule-associated component (SMAC) has a periodicity of 6.4 nm and extends with each 2-membered rootlet posteriorly into the cell. One 5-membered rootlet passes very near the eyespot. Phylogeny in green algal motile cells is discussed. 相似文献
57.
The effect of caffeine on Chinese hamster V79 cells after treatment with the highly mutagenic (+/-)-7 beta,8 alpha-dihydroxy-9 alpha, 10 alpha-7,8,9,10-tetrahydrobenzo[a]pyrene, and the weaker mutagen (+/-)-7 beta,8 alpha-dihydroxy-9 beta,10 beta-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, B[a]P-deiol-epoxide II, was studied at both the biological and molecular levels. Caffeine, at nontoxic dose levels, caused a synergistic reduction in cell survival induced by both isomers and also inhibited DNA elongation as measured by alkaline sucrose-gradient analysis of nascent DNA. However, caffeine did not affect the induction of either ouabain-resistant mutants or sister-chromatid exchanges by either isomer. These results suggest that enhanced cell killing by caffeine in benzo[a]pyrene-diol-epoxide treated V79 cells may be related to caffeine's inhibitory effect on DNA elongation. However, inhibition of DNA elongation by caffeine did not influence the resulting induced levels of mutagenesis or sister-chromatid exchanges. 相似文献
58.
T Raposa 《Mutation research》1978,57(2):241-251
The effect of various cytostatic drugs was studied on the frequency of sister chromatid exchanges (SCEs) in vitro and in PHA-stimulated lymphocytes of leukaemic patients under cytostatic therapy. The lymphocyte system is a sensitive one for the detection of DNA damage after administration of cytostatic drugs in vitro. Mitomycin C, busulphan, vincristine, chlorambucil, cytosine arabinoside, cyclophosphamide and lycurim were tested. All except cyclophosphamide induced high frequencies of SCEs in the first mitosis after their administration. The experiments with PHA-stimulated lymphocytes in vivo from patients treated with cytostatics showed that cytosine arabinoside, in combination with thioguanine, did not induce higher frequencies of SCEs, whereas in patients who were treated with cyclophosphamide alone or in combination with other cytostatic drugs, there was a higher incidence of SCEs during treatment. About 10 days after the termination of the treatment the elevated freuqencies of SCEs returned to the initial level. After administration of some mutagens, especially alkylating agents in vivo, the lymphocyte system can be used to assess induced DNA repair by continuously monitoring for SCEs. 相似文献
59.
Rajinder S. Dhindsa 《Planta》1978,141(3):269-272
The effects of 5-bromo-2-deoxyuridine (BUdR, thymidine analogue), AMO-1618 (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride), a growth retardant, and p-chlorophenoxyisobutyric acid (PCIB, an antiauxin) on growth (dry weight increase) and fiber development in unfertilized cotton (Gossypium hirsutum L.) ovules grown in vitro have been studied. BUdR (5 M) causes about 70% inhibition of fiber production, with little effect on ovule growth, if applied during the first 6 d of culture in the presence of GA3 and IAA. AMO-1618, when used with GA3 alone, causes only a small reduction in both dry weight and fiber production, but when used with IAA alone reduces both fiber production and dry weight, the effect on the latter being predominant. In the presence of both IAA and GA3, AMO-1618 causes a small decrease in fiber production but a major decrease in dry weight. PCIB completely inhibits fiber growth but has little effect on dry weight, especially when GA3 is present. These results indicate that GA3 mainly promotes ovule growth while IAA is largerly responsible for fiber growth.Abbreviations AMO-1618
2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride
- BUdR
5-bromo-2-deoxyuridine
- GA3
gibberellic acid
- IAA
indole-3-acetic acid
- PCIB
p-chlorophenoxyisobutyric acid
- TFU
total fiber units 相似文献
60.
A simple double-isotope procedure has been developed for making simultaneous measurements of bound Ca2+ and relative force in glycerinated rabbit psoas bundles containing two fibers. With this preparation it is possible to study Ca2+-troponin interactions coincident with MgATP-induced force development. Over the free [Ca2+] range 6 · 10?8–1.2 · 10?5 M the bound Ca2+ varied from 0.25 to 1.65 μmol/g protein. The free [Ca2+] at half-maximal Ca2+ saturation was 2 · 10?7 M while that a half-maximal force was 5 · 10?7 M. Half-maximal Ca2+ saturation was associated with 20% maximal force. The force-[Ca2+] saturation curve showed a steep rise in slope at greater than half saturation. The observed relationship was consistent with a model in which multiple occupancy of troponin Ca2+-binding sites is essential for initiation of cross-bridge cycling. 相似文献