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951.
Continuous production of l(+)-lactic acid by Lactobacillus casei in two-stage systems 总被引:2,自引:0,他引:2
Bruno-Bárcena JM Ragout AL Córdoba PR Siñeriz F 《Applied microbiology and biotechnology》1999,51(3):316-324
A two-stage two-stream chemostat system and a two-stage two-stream immobilized upflow packed-bed reactor system were used
for the study of lactic acid production by Lactobacillus casei subsp casei. A mixing ratio of D
12/D
2 = 0.5 (D = dilution rate) resulted in optimum production, making it possible to generate continuously a broth with high lactic acid
concentration (48 g l−1) and with a lowered overall content of initial yeast extract (5 g l−1), half the concentration supplied in the one-step process. In the two-stage chemostat system, with the first stage at pH
5.5 and 37 °C and a second stage at pH 6.0, a temperature change from 40 °C to 45 °C in the second stage resulted in a 100%
substrate consumption at an overall dilution rate of 0.05 h−1. To increase the cell mass in the system, an adhesive strain of L. casei was used to inoculate two packed-bed reactors, which operated with two mixed feedstock streams at the optimal conditions
found above. Lactic acid fermentation started after a lag period of cell growth over foam glass particles. No significant
amount of free cells, compared with those adhering to the glass foam, was observed during continuous lactic acid production.
The extreme values, 57.5 g l−1 for lactic acid concentration and 9.72 g l−1 h−1 for the volumetric productivity, in upflow packed-bed reactors were higher than those obtained for free cells (48 g l−1 and 2.42 g l−1 h−1) respectively and the highest overall l(+)-lactic acid purity (96.8%) was obtained in the two-chemostat system as compared with the immobilized-cell reactors (93%).
Received: 4 December 1997 / Received revision: 23 February 1998 / Accepted: 14 March 1998 相似文献
952.
The gene dak1 encoding a dihydroxyacetone kinase (DHAK) isoenzyme I, one of two isoenzymes in the Schizosaccharomyces pombe IFO 0354 strain, was cloned and sequenced. The dak1 gene comprises 1743 bp and encodes a protein of 62 245 Da. The deduced amino acid sequence showed a similarity to a putative
DHAK of Saccharomyces cerevisiae and DHAK of Citrobacter freundii. The dak1 gene was expressed at a high level in Escherichia coli, and the recombinant enzyme was purified to homogeneity and characterized. The acetone powder of recombinant E. coli cells was used to produce dihydroxyacetone phosphate.
Received: 25 August 1998 / Received revision: 22 September 1998 / Accepted: 11 October 1998 相似文献
953.
The Drosophila fat facets gene encodes a deubiquitinating enzyme required during eye development to limit the number of photoreceptors in each facet to eight. Ubiquitin is a small polypeptide that targets proteins for degradation by the proteasome. Deubiquitinating enzymes cleave ubiquitin-protein bonds. In order to investigate the role of FAT FACETS in the ubiquitin pathway, genetic interactions between fat facets and the Drosophila UbcD1 gene were assessed. In addition, three yeast deubiquitinating enzyme genes were tested for their ability to substitute for fat facets in the developing Drosophila eye and for their effects on eye morphology. The results of these experiments support the hypothesis that FAT FACETS activity antagonizes that of the proteolytic machinery. The implications of these results for the specificity of FAF and yeast UBPs are discussed as well. 相似文献
954.
Coupling of the cell cycle and myogenesis through the cyclin D1-dependent interaction of MyoD with cdk4
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Proliferating myoblasts express the muscle determination factor, MyoD, throughout the cell cycle in the absence of differentiation. Here we show that a mitogen-sensitive mechanism, involving the direct interaction between MyoD and cdk4, restricts myoblast differentiation to cells that have entered into the G0 phase of the cell cycle under mitogen withdrawal. Interaction between MyoD and cdk4 disrupts MyoD DNA-binding, muscle-specific gene activation and myogenic conversion of 10T1/2 cells independently of cyclin D1 and the CAK activation of cdk4. Forced induction of cyclin D1 in myotubes results in the cytoplasmic to nuclear translocation of cdk4. The specific MyoD-cdk4 interaction in dividing myoblasts, coupled with the cyclin D1-dependent nuclear targeting of cdk4, suggests a mitogen-sensitive mechanism whereby cyclin D1 can regulate MyoD function and the onset of myogenesis by controlling the cellular location of cdk4 rather than the phosphorylation status of MyoD. 相似文献
955.
Wang L Liu Q Frutos AG Gillmor SD Thiel AJ Strother TC Condon AE Corn RM Lagally MG Smith LM 《Bio Systems》1999,52(1-3):189-191
DNA computing on surfaces is where complex combinatorial mixtures of DNA molecules are immobilized on a substrate and subsets are tagged and enzymatically modified (DESTROY) in repeated cycles of the DNA computation. A restriction enzyme has been chosen for the surface DESTROY operation. For the READOUT operation, both cycle sequencing and PCR amplification followed by addressed array hybridization were studied to determine the DNA sequences after the computations. 相似文献
956.
肾脏和肾神经在应激、钠盐所致高血压中的作用 总被引:16,自引:1,他引:15
本工作采用电生理、生化、放免、电镜等方法,探讨了慢性应激和盐致高血压大鼠交感神经系统和肾脏功能的改变。实验在雄性SD大鼠上进行。结果表明:(1)高盐大鼠肾血浆流量(RPF)和尿钠排泄明显增加,而应激大鼠RPF显著下降。(2)电镜显示高盐大鼠近曲和远曲小管上皮细胞及线粒体变大,应激则使细胞萎缩、线粒体变小。(3)高盐大鼠肾皮质NaKATP酶活性下降,应激可使其恢复。(4)频谱分析显示应激大鼠低频波动(02~09Hz)明显增加。(5)应激导致大鼠肾素活性(PRA)及血管紧张素Ⅱ(ANGⅡ)水平升高,并能使高盐大鼠低PRA和ANGⅡ水平升高。(6)大鼠去除双侧肾神经后,应激无法造成血压升高、RPF下降和PRA、ANGⅡ上升。上述结果提示:肾交感神经系统兴奋性增加介导的肾脏机制,可能在应激和/或盐致高血压发病过程中具有重要作用。 相似文献
957.
在离体大鼠小脑脑片上观察了组胺对小脑皮层第Ⅹ小叶浦肯野细胞的作用。组胺(3~100μmol/L)主要引起浦肯野细胞的兴奋反应(944%,51/54),在少数细胞上也观察到组胺所引起的放电抑制现象(56%,3/54)。用低Ca2+/高Mg2+人工脑脊液灌流脑片,不能取消浦肯野细胞对组胺的兴奋反应(n=4)。H2受体对抗剂ranitidine(01~5μmol/L)能够阻断浦肯野细胞对组胺的兴奋反应(n=20),而H1受体对抗剂triprolidine(05~5μmol/L)不能够(n=9)或仅轻微地(n=4)阻断浦肯野细胞对组胺的兴奋反应。这些结果提示,组胺可能主要通过H2受体的介导对浦肯野细胞起兴奋性调节作用,下丘脑小脑组胺能神经通路可能参与了小脑的某些躯体的和非躯体的功能调节。 相似文献
958.
To investigate the possible mechanisms underlying the difference of NMDA and non-NMDA receptors in spinal nociception originating in skin and muscle, release of aspartate (Asp) and glutamate (Glu) in the spinal dorsal horn was detected by stimulation of cutaneous and muscular nerves in cats using microdialysis technique. Asp and Glu were increased respectively by (323 +/- 55)% and (169 +/- 16)% following stimulation of cutaneous nerve, but by (150 +/- 16)% and (218 +/- 42)% respectively following stimulation of muscular nerve. Asp increase was approximately three times higher than that of Glu following cutaneous nerve-stimulation (P < 0.01), while Glu increase was approximately twice as high as that of Asp following muscular nerve-stimulation (P < 0.05). It is likely that nociceptive cutaneous and muscular inputs preferentially elicite release of Asp and Glu respectively, resulting in a functional differentiation of NMDA and non-NMDA receptor in the mediation of different nociceptive information. 相似文献
959.
It has been estimated that eukaryotes carry more than 50 genes for tRNA modifying enzymes. Of the few so far identified most come from yeast, a lower eukaryote. In Saccharomyces cerevisiae, the TRM1 gene is a nuclear gene encoding the tRNA(m2/ 2G(26))dimethyltransferase, which catalyses the formation of the N2, N2-dimethylguanosine at position 26 in tRNA. We have isolated and characterized the corresponding gene ZC376.5 in Caenorhabditis elegans. Via RTPCR the cDNA sequence of the full length ZC376.5 has now been cloned, expressed in Escherichia coli and demonstrated to encode a tRNA(m2/2G(26))dimethyltransferase that produces dimethyl-G26 in vivo and in vitro with tRNA from yeast and bacteria as substrates. This is the first example of a complete gene sequence coding for a tRNA modifying enzyme from a multicellular organism. A point mutation in exon IV in the C. elegans genome sequence coding for the tRNA(m2/2G(26))methyltransferase that substituted arginine246 for glycine eliminated the modification activity. Exchanging the corresponding lysine residue in the yeast Trm1p for alanine caused a severe loss of activity, indicating that the identity of the amino acid at this position is important for enzyme activity. 相似文献
960.