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991.
Michael D. Papagiannis 《Origins of life and evolution of the biosphere》1984,14(1-4):43-50
It is generally thought that the Universe started with a big explosion (Big Bang) approximately 15 billion years ago. Hydrogen and helium were formed within the first few minutes, while all the other chemical elements are the by-products of stellar evolution that are added to the interstellar medium through the supernova explosions of the larger stars. Carbon, Oxygen, Hydrogen and Nitrogen, which constitute about 98% of the biomass of the Earth, are also among the most abundant chemical elements in the Universe. A seemingly unique combination of the fundamental laws and constants of the Universe made possible the origin and subsequent slow evolution of life. 相似文献
992.
Clostridium thermocellum: Adhesion and sporulation while adhered to cellulose and hemicellulose 总被引:1,自引:0,他引:1
Summary During growth in the presence of fibers composed of cellulose or hemicellulose, various strains of the thermophilic soil bacterium Clostridium thermocellum and several newly isolated thermophilic anaerobic soil bacteria adhered to the fibers. Attachment occurred via a fibrous ruthenium red-staining material. C. thermocellum sporulated while attached to the fibers when the pH dropped below 6.4. It is postulated that the attachment is involved in cellulose breakdown and that C. thermocellum gaines an advantage by remaining attached to its insoluble substrates when the environment is not suitable for rapid growth. The tendency to adhere to cellulose fibers was used in the purification of thermophilic cellulolytic anaerobes. 相似文献
993.
Michael J. Hall Louis J. Nisbet Donald Westmacott Philippe Wong-Kai-In 《Journal of microbiological methods》1984,2(4):203-214
Roche Susceptibility Test (RST) Medium represents the most completely optimized and convenient fully defined medium described. It requires no post-autoclaving supplementation with vitamins, supports good growth of all common aerobic and anaerobic pathogens and may be used as a broth or agar gel on which the swarming of Proteus spp. is virtually eliminated. The broth as a superior buffering capacity to most complex media and an osmolality and pH close to those of human serum. RST is highly satisfactory for the susceptibility testing of commonly used antibiotics and meets the requirements of the National Committe for Clinical Laboratory Standards of the U.S.A. in almost every respect. 相似文献
994.
Bacterial cells have three phases of growth which are characterized respectively by: (1) balanced growth with a high yield of biomass; (2) balanced growth with lower biomass yield; and (3) unbalanced growth with lowest biomass yield. Phases 2 and 3 are associated with elevated concentrations of the regulatory nucleotides centered on guanosine-5′-diphosphate-3′-diphosphate. Maintenance of the correct growth phase is important in optimizing industrial product formation by bacterial populations. 相似文献
995.
Michael Ma Shuenn-Jue Wu Maureen Howard Alexej B. Borkovec 《In vitro cellular & developmental biology. Plant》1984,20(9):739-742
Summary We report here that the use of murine thymoma cell EL-4 conditioned medium enhances hybridoma yield in a low-antigen dose
in vitro immunization protocol. This improved protocol allowed the production of a panel of monoclonal antibodies toDrosophila yolk proteins using less than 1 nanomole of antigen. We believe this refinement will be valuable for the application of hybridoma
technology to biologically active materials that are hard to isolate and purify due to their low concentration in the biological
fluids.
This research was supported by the College of Agriculture and Life Sciences, University of Maryland, USDA-University of Maryland
Cooperative
Editor's Statement This observation should simplify in vitro immunization approaches and shed new light on the factors required
for the in vitro immune response. Wallace L. McKeehan 相似文献
996.
Shu’a Yagev Michael Heller Arié Pinson 《In vitro cellular & developmental biology. Plant》1984,20(12):893-898
Summary Postnatal rat heart cells in culture enriched with respect to muscle cells were obtained by either high density seeding or
by the replating technique. [3H]Thymidine incorporation to DNA and the enzymatic pattern of cytoplasmic and lysosomal enzymes have been studied as a function
of the culture’s age, of seeding density, and replating. It was shown that (a) replating maintains predominance of myocyte
population for at least 2 wk in culture; (b) heavy seeding density allows homogeneous myocyte population for the 1st wk in
culture; and (c) the enzyme profile of the culture may serve as an indicator for the type of cell population in culture and
its state of differentiation.
This study was done as partial fulfilment of the M.Sc. thesis in Biochemistry (SY). Supported by grants from The Chief Scientist,
Ministry of Health, State of Israel; The Ministry of Education and Sciences, State of Niedersachssen (FRG); and The Foundation
for Heart Research from Mr. and Mrs. D. Vidal-Madjar, Paris, France. 相似文献
997.
Marjorie A. Jones Catherine J. Norris Michael J.K. Harper 《Prostaglandins & other lipid mediators》1984,28(1)
The prostaglandin (PG) content of several tissues and fluids from 6 day pregnant rabbits was evaluated following treatment with indomethacin or vehicle
. PGE and PGF were measured by radioimmunoassay. More complete depletion of PGE and PGF was accomplished by 3 injections of indomethacin (s.c.) given during the 18 h before sacrifice at a dose of 10 mg indomethacin per kg body weight than was accomplished by 1 injection of the same amount of indomethacin (i.v.) 1.5 h before sacrifice. Levels of PGF were more easily depressed by indomethacin than were those of PGE. PG levels in the kidney and blastocysts were depressed to a greater extent by indomethacin than were those in the uterus, uterine fluid or peritoneal fluid. Evaluation of the effect of indomethacin on a particular physiological function should be interpreted with caution unless the extent of PG depletion in that tissue is also measured. 相似文献
998.
Michael J. Barber Andrew S. Zektzer Gerald M. Rosen Helen A. Demos Elmer J. Rauckman 《生物化学与生物物理学报:生物膜》1984,776(1):159-168
Hepatic microsomal membranes, prepared under various conditions that yield either ‘intact’ or ‘disrupted’ microsomal vesicles, have been labeled via the sulfhydryl groups of intrinsic membrane proteins using nitroxide analogs of . Electron paramagnetic resonance spectra revealed the presence of two dominant classes of bound label corresponding to differing degrees of immobilization, the ratio of which were quantitated using a parameter designated the ‘’ ratio. For latent microsomes, the value of this parameter was determined to be and was influenced by factors such as label/protein ratio, incubation period, nitroxide structure, temperature and pH. The ratio was also sensitive to the degree of membrane integrity as revealed by the latency of mannose 6-phosphate activity of glucose-6-phosphohydrolase. In addition, membrane disruption resulted in a corresponding decrease in the order parameter for nitroxide-labeled fatty acids intercalated within the lipid bilayer. The ratio was observed to be dependent upon the method of microsome preparation yielding values of for ‘hypertonically disrupted’ vesicles and for ‘mechanically disrupted’ vesicles. Microsomal marker enzymes such as cytochrome and FAD-containing monooxygenase retained significant levels of functionally following nitroxide incorporation. 相似文献
999.
The H2 uptake activity (units/mg protein) of Clostridium pasteurianum cells with methylene blue as the electron acceptor increases with cell density independent of the growth conditions. The H2 evolution activity (units/mg protein) of the same cells with reduced methyl viologen as the electron donor remains fairly constant under all growth conditions tested. Cells grown under N2-fixing conditions have the highest H2 uptake activity and were used for the purification of hydrogenase II (uptake hydrogenase). Attempts to separate hydrogenase II from hydrogenase I (bidirectional hydrogenase) by a previously published method were unreliable. We report here a new large-scale purification procedure which employs a rapid membrane filtration system to fractionate cell-free extracts. Hydrogenases I and II were easily filtered into the low-molecular-weight fraction (Mr less than 100 000), and from this, hydrogenase II was further purified to a homogeneous state. Hydrogenase II is a monomeric iron-sulfur protein of molecular weight 53 000 containing eight iron atoms and eight acid-labile sulfur atoms per molecule. Hydrogenase II catalyzes both H2 oxidation and H2 evolution at rates of 3000 and 5.9 μmol H2 consumed or evolved/min per mg protein, respectively. The purification procedure for hydrogenase II using the filtration system described greatly facilitates the large-scale purification of hydrogenase I and other enzymes from cell-free extracts of C. pasteurianum. 相似文献
1000.
Three distinct states can be identified for cells of the green alga Chlorella vulgaris; State 1 and State 2 obtained by preillumination in far-red and red light, respectively, and the dark state obtained by dark-adaptation. Addition of the inhibitor DCMU to algal cells leads to an initial rapid increase in chlorophyll-a fluorescence reflecting the closure of Photosystem II traps. This, in the case of dark and state-2-adapted algae is followed by a slow light-dependent increase to a fluorescence yield typical of State-1-adapted cells. Measurements of low temperature (77 K) emission spectra indicate that the low fluorescence yields of dark and State-2-adapted algae reflect similar balances in excitation-energy distribution between the two photosystems. In both cases, the balance favours PS I and the slow fluorescence increase seen in the poisoned algae reflects a redressing of this balance in favour of PS II. The low fluorescence yield of State-2-adapted algae is thought to be associated with the phosphorylation of chlorophyll a/b light-harvesting protein (Biochim. Biophys. Acta (1983) 724, 94–103). Measurements of the uncoupler and ATPase sensitivity of the light-dependent increases seen in DCMU-poisoned cells indicate that the low fluorescence yield of dark-adapted algae is of different origin. Evidence is presented showing that the light-driven changes in excitation-energy distribution seen in green algae involve two distinct processes; a low-intensity, wavelenght-independent change reflecting simple light/dark changes and a higher intensity, wavelength-dependent change reflecting State 1/State 2 adaptation. The former changes appear to be associated with changes in the local ionic environment within the algal chloroplast, whilst the latter appear to reflect changes in the phosphorylation state of chlorophyll a/b light-harvesting protein. 相似文献