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71.
V. M. Chavez R. E. Litz P. A. Moon K. Norstog 《In vitro cellular & developmental biology. Plant》1992,28(2):59-63
Summary Embryogenic callus was induced from explanted pinnae of newly emerged leaves of mature plants ofCeratozamia mexicana var. Robusta (Gymnospermae, Cycadales) on a modified B5 formulation with 1 mg·liter−1 kinetin and 1 mg·liter−1 2,4-dichlorophenoxyacetic acid. Proembryos developed on induction medium, but they were more numerous after subculture onto
phytohormone-free medium, which also enabled suspensors to elongate. For nearly 1.5 yr after explanting, subsequent development
of somatic embryos was not observed as suspensors dedifferentiated to form embryogenic callus on phytohormone-free medium.
After this time, cotyledonary somatic embryos developed at the distal end of the suspensors. Somatic embryos have germinated
on phytohormone-free medium. This is the first report of regeneration by somatic embryogenesis of a gymnosperm species from
a mature tree. This technique has great potential for preservation of the highly endangered cycads. 相似文献
72.
S.A. LEAROYD, R.G. KROLL AND C.F. THURSTON. 1992. The rates of reduction of seven redox dyes by 13 bacterial strains were measured and found to vary greatly between different bacterium/dye combinations. Phenazine ethosulphate and toluidine blue were the most rapidly reduced dyes by the majority of bacteria and resorufin and 2-hydroxy-1,4-naphthoquinone were reduced slowly, if at all. There was also considerable variation in the rates of reduction with any single dye/organism combination. Glucose stimulated the rates of endogenous dye reduction in about half of the organisms. For Bacillus cereus, Pseudomonas fluorescens and Escherichia coli , dye reduction was stimulated by a range of exogenous substrates but lactose, the primary available carbon and energy source in milk, had little effect. In Lactococcus lactis , dye reduction was stimulated by sugars but not by organic acids. Oxygen successfully competed with dye reduction in organisms containing respiratory chains, but with membrane fractions, dye reduction was more rapid than oxygen consumption. All the organisms showed little cytosolic dye reduction, except L. lactis which showed substantial rates of reduction of some dyes by this fraction. With the membrane fraction of E. coli and Ps. fluorescens , cyanide inhibited NADH and succinate-dependent dye reduction, Antimycin A inhibited lactate and succinate and rotenone had no significant effect, but inhibition was not always observed with membrane from both organisms. 相似文献
73.
This research involves the development and evaluation of a part flow control model for a type of flexible manufacturing system (FMS) called a dedicated flexible flow line (FFL). In the FFL, all part types flow along the same path between successive machine groups. The specific objective of the part flow control model for the FFL is to minimize makespan for a given set of parts produced in a FFL near-term schedule, given fixed available buffer constraints. The control model developed in this research involved the repeated, real-time execution of a mathematical programming algorithm. The algorithm attempts to release the right mix of parts at the tight time to keep the FFL operating smoothly. The focus of the approach is directed toward managing WIP buffers for each machine group queue. The algorithm specifically incorporates stochastic disturbance factors such as machine failures. Through a limited number of simulation experiments, performance of the control model is shown to be superior to other parts releasing and control methods reported in the literature. 相似文献
74.
75.
Nuclear interactions of retinoic acid-binding protein in chemically induced mammary adenocarcinoma. 总被引:3,自引:0,他引:3 下载免费PDF全文
Cellular retinoic acid-binding protein (CRABP) was detected in the nuclear fraction of N-methyl-N-nitrosourea-induced mammary cancers after the incubation of cytosol containing [3H]retinoic acid (RA)-bound CRABP with isolated nuclei. CRABP extracted from the nuclei in buffer containing 0.4 M-KCl sedimented as a 2 S component when subjected to sucrose-density-gradient analysis. [3H]RA-CRABP was found to be a prerequisite for the detection of nuclear binding, since the incubation of isolated nuclei or 0.4 M-KCl extract of the nuclei with [3H]RA did not result in any significant binding. Incubation of [3H]RA-CRABP at 25 or 30 degrees C before incubation with the nuclei neither altered the sedimentation coefficient nor enhanced the nuclear binding compared with 0 degrees C incubation. The tumour nuclei contained a saturable number of binding sites with a dissociation constant of 1.6 x 10(-9) M. These results indicate that the action of retinoic acid in the target organ may be mediated by its interaction with the nuclei. 相似文献
76.
The Crustacea of some chalk streams in southern England 总被引:1,自引:1,他引:0
Stephanie F. Ham 《Hydrobiologia》1982,97(3):193-201
Records of Crustacea from chalk streams in southern England are described. Classification of sites suggested that flow regime was an important influence on the fauna and the distribution of individual species are discussed in this respect. 相似文献
77.
A modified latex agglutination (LA) test was compared with Gram-staining and counterimmunoelectrophoresis (CIE) for the rapid detection in the cerebrospinal fluid (CSF) of antigen to Haemophilus influenzae type b, Neisseria meningitidis groups A, B and C, Escherichia coli K1, Streptococcus pneumoniae and group B streptococci, seven frequent causes of bacterial meningitis in children. Of 50 CSF samples from patients with culture-proven bacterial meningitis 90% were correctly shown by the LA test to contain antigen of the responsible organism. Gram-staining revealed organisms in 80% of 45 of these samples. In 75% of the 40 samples that were of sufficient volume for CIE, positive results for the appropriate antigen were obtained. The concentration of antigen detected in the CSF by the LA test varied from undetectable to 800 000 ng/ml. Patients with a high concentration (more than 2000 ng/ml or a positive result at dilutions of CSF over 1/8) were significantly more likely to have a poor response to therapy (two died and two had persistent pleocytosis or bacteria in the CSF) than patients with a lower concentration (4/16 v. 0/18, P < 0.05). After appropriate therapy was begun the concentration of antigen fell dramatically, but measurable amounts of antigen persisted in the CSF for up to 6 days. The LA test detected bacterial antigen at concentrations 2 to 70 times below the lower limit detected by CIE. In seven additional patients who had received antibiotics before lumbar puncture was performed the LA test detected antigen from meningitis-causing bacteria even though cultures of the CSF were sterile. In another 145 patients who did not have meningitis the results of the LA test were negative. The LA test, done as described in this article, is easier to perform than CIE and should be a useful addition to the diagnostic tests carried out on the CSF of any patient suspected of having meningitis. 相似文献
78.
Stephanie Gordon Phillips Shiu-Lan Lui David M. Phillips 《In vitro cellular & developmental biology. Plant》1982,18(8):727-738
Summary Epithelial cells may relate to their basement membrane substrates via lectin-like interactions. In a model system for study
of this type of interaction, lectin-coated bacteriological plastic petri dishes were presented as substrates for epithelial
cell adhesion. Of 21 lectins tested by mixed agglutination against two epithelial cell types, Madin-Darby canine kidney (MDCK),
and human embryonic kidney cells (HEK), nine gave less than 5% rosettes and 12 gave 5 to 50% rosettes. Wheat germ agglutinin
(WGA) andGeodia cydonium lectin gave the highest percentage of rosettes. Wheat germ agglutinin was readily adsorbed to plastic surfaces and maintained
specificity in binding interactions. Both MDCK and HEK cells attached as well to WGA coated petri dishes as to conventional
tissue culture dishes. Furthermore, both spread over the lectin-coated surfaces. The MDCK cells grew to confluence and could
be subcultured and maintained indefinitely on such surfaces, although WGA in solution was toxic to the cells in concentrations
as low as 0.1 to 1.0 μg/ml. Cell attachment to WGA coated dishes was blocked by cycloheximide only if the cells had been preincubated
with the inhibitor for several hours. Cell attachment was not inhibited by pretreatment of cells with neuraminidase. Precoating
cells with WGA blocked binding to both WGA-coated surfaces and untreated tissue culture dishes. Cells attached to WGA-coated
dishes could not be readily dislodged by trypsin-EDTA for the first 2 h after subculture. By 4 h, attachment was again trypsin
sensitive, suggesting that the cells synthesized a trypsin-sensitive material that was laid down between the cell surface
and the WGA-coated dish. Regeneration of trypsin sensitivity was not blocked by cycloheximide.
This work was supported by Research Grant AG01986 from the National Institutes of Health, Bethesda, Maryland. 相似文献
79.
Synthetic leukotrienes (LT) C4 and D4 elicited concentration-dependent contractions of the guinea pig uterus between 10?8-10?6M, whereas LTE4 appeared 1000-fold weaker. The potencies of LTC4 and LTD4 were similar to that of acetylcholine and PGF2α but weaker than that of PGE2. The maximal contractions elicited by LTC4 and LTD4 were 66.0 ± 2.1% and 63.8 ± 4.6% that elicited by acetylcholine. FPL 55712 (10?5M) antagonized the uterine contractile activity of LTD4, while meclofenamic acid at 10?5M but not at 10?6M also antagonized the LTD4-induced contration. Radioimmunoassay of the uterine tissue bathing fluid following LTD4 indicated the variable presence of low concentrations of PGE2, PGF2α and TXB2. These results demonstrate the LTC4 and LTD4 possess significant uterine contractile activity, which may only partially be mediated indirectly via prostaglandin products. 相似文献
80.
Distribution ratios (intracellular/extracellular concentration) of α-amino isobutyric acid (AIB) and activities of the transaminases of alanine (Ala AT), aspartate (Asp AT), leucine (Leu AT) and glutamate dehydrogenase (GDH) were determined in tissues of freshly caught plaice, Pleuronectes platessa , deprived of food for three months. Liver, red muscle and white muscle demonstrated increased distribution ratios for AIB, while the ratios decreased in kidney and gill with deprivation. Values of the distribution ratio were below 1.0 only in white muscle, with kidney and liver having the highest absolute values. Transaminase activities generally rose with deprivation in all tissues, although the absolute increases were greatest in liver and for the two enzymes Ala AT and GDH. These data indicate that with food deprivation, the role of the liver in amino acid metabolism is maintained and slightly enhanced, while that of the kidney is reduced. Both muscle types (red and white) showed increased water content implicating protein mobilization which could enhance the availability of amino acids for liver gluconeogenesis and metabolite sparing in other tissues during conditions of depletion. 相似文献