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971.
972.
We have evaluated surface plasmon resonance with avidin-biotin immobilized liposomes tocharacterize membrane binding of ubiquitous mitochondrial creatine kinase (uMtCK). Whilethe sarcomeric sMtCK isoform is well known to bind to negatively charged phospholipids,especially cardiolipin, this report provides the first experimental evidence on the membraneinteraction of an uMtCK isoform. Qualitative measurements showed that liposomes containing16% (w/w) cardiolipin bind octameric as well as dimeric human uMtCK and also cytochromec, but not bovine serum albumin. Quantitative parameters could be derived only for themembrane interaction of octameric human uMtCK using an improved analytical approach.Association and dissociation kinetics of octameric uMtCK fit well to a model for heterogeneousinteraction suggesting two independent binding sites. Rate constants of the two sites differedby one order of magnitude, while their affinity constants were both about 80–100 nM. Thedata obtained demonstrate that surface plasmon resonance with immobilized liposomes is asuitable approach to characterize the binding of peripheral proteins to a lipid bilayer and thatthis method yields consistent quantitative binding parameters. 相似文献
973.
Ralf T. Otto Holger Scheib Uwe T. Bornscheuer Jü rgen Pleiss Christoph Syldatk Rolf D. Schmid 《Journal of Molecular Catalysis .B, Enzymatic》2000,8(4-6):201-211
Arylaliphatic glycolipids are known for their pharmaceutical and medicinal properties. We found that a great variety of arylaliphatic esters can be synthesized from non-activated substrates like glucose or the natural occurring drug salicin using lipase B from Candida antarctica (CAL-B). However, esters based on aromatic carboxylic acids or unsaturated arylaliphatic acids, like cinnamic acid and its derivatives, which are known to display anticancer activity, could not be obtained. In this work, we performed computer-aided molecular modeling based on data of our work published recently and syntheses of new glycolipids to understand why some substances are accepted by CAL-B while some are not. For this purpose, we investigated the accessibility of the lipase binding site for the arylaliphatic acyl donors as well as the steric interactions between the aglycons of glucosides and the residues of the alcohol binding pocket in order to elucidate potentials and limitations of CAL-B for the synthesis of aromatic glycolipids. 相似文献
974.
Summary A metatheoretical and historiographical re-analysis of the Evolutionary Synthesis (the process) and the Synthetic Theory (the
result) leads to the following conclusion: The Synthetic Theory is not a reductionistic, but rather a structuralistic theory
with a limited range of relevant hierarchical levels. Historically the Synthesis was not a sudden event but a rational long-term
project carried out between 1930 and 1950 by a large number of biologists in several countries. In the second part of our
paper the contributions of several German biologists to the Synthesis are analyzed. 相似文献
975.
Schlattner Uwe Forstner Michael Eder Michael Stachowiak Olaf Fritz-Wolf Karin Wallimann Theo 《Molecular and cellular biochemistry》1998,184(1-2):125-140
Mitochondrial creatine kinase (Mi-CK) is a central enzyme in energy metabolism of tissues with high and fluctuating energy requirements. In this review, recent progress in the functional and structural characterization of Mi-CK is summarized with special emphasis on the solved X-ray structure of chicken Mib-CK octamer (Fritz-Wolf et al., Nature 381, 341-345, 1996). The new results are discussed in a historical context and related to the characteristics of CK isoforms as known from a large number of biophysical and biochemical studies. Finally, two hypothetical functional aspects of the Mi-CK structure are proposed: (i) putative membrane binding motifs at the top and bottom faces of the octamer and (ii) a possible functional role of the central 20 Å channel. 相似文献
976.
977.
978.
Summary The various types of human primary spermatocytes were classified by means of morphological and morphometrical studies. Based on this classification, the topographic arrangement of the spermatocyte populations in the longitudinal course of seminiferous tubules was determined. This analysis revealed human spermatogenesis be to subjected to a complex local plan of organization, which is based upon the geometry of spirals.The centers of gravity of spermatocyte populations of subsequent degrees of differentiation are arranged on he lices that are contracted conically to the lumen of the seminiferous tubule. On these helices the centers of gravity of the populations diverge continuously 173.8°+/-32.4°. Populations of the same degrees of development are arranged on helices with constant diameters. On these helices the centers of gravity of the populations diverge continuously 142.6°+/-14.2°.The present results lead to new aspects of the kinetics and morphogenesis of the seminiferous epithelium, which can be integrated into a comprehensive biological concept. 相似文献
979.
Biogeochemistry of Late Paleozoic North American brachiopods and secular variation of seawater composition 总被引:3,自引:0,他引:3
Uwe Brand 《Biodegradation》1989,7(3):159-193
Sr/Ca ratios in modern brachiopod shells reflect variations in ambient seawater, whereas their Na contents show no relationship
with water depth or habitat. Their Mn and Fe contents are controlled, in part, by leaching of these elements from oxide coatings
or the low input/sedimentation rate of detrital material into depositional areas such as Quatsino Sound.
For most Carboniferous brachiopods from North America, the Mn and Fe contents are similar to those recorded by their Recent
counterparts. The high Mn and Fe contents in the brachiopods from shales suggest several possibilities for these levels. One
possibility is the leaching of Mn and Fe from oxide coatings/matrix which was not completely removed in the cleaning process,
or the high levels in part reflect unusual depositional conditions (some degree of anoxia) for the local shaly environments.
The Sr/Ca ratio of brachiopods and, by inference, complementary seawater, did not vary significantly during the Carboniferous.
The Sr/Ca minimum observed in brachiopods of Mississippian age coincides with a dip in the 87Sr/86Sr curve and correlates with the Hercynian orogeny. This is attributed to the cycling of seawater through mid-ocean ridge
basalts, and postulated exchange reactions account for variation in the composition of seawater-Ca. The unidirectional trend
of heavier δ13C values from the Devonian to the Permian is intricately coupled with the evolution of the terrestrial biomass. In addition
to expansion of terrestrial plants, burial of reduced carbon in the form of coal (organic matter) contributed to the observed
shift. The start of the Permo-Pennsylvanian glaciation is marked by a negative excursion of the secular carbon trend, which
is linked to weathering of reduced carbon and its return to the oceanic reservoir with its oxidized carbon. The oxygen isotope
values reflect the unidirectional trend towards higher values of the carbon data with decreasing geologic age. Negative excursions
of the trend may be related to extensive weathering of terrestrial and submarine rocks, whereas positive excursions may be
related to hydrothermal alteration of submarine rocks and dehydration of oceanic crust during times of active sea-floor spreading.
Oxygen-calculated water temperatures of unaltered brachiopod material are unrealistically high for all of the Devonian, and
the Chesterian-Meramecian, Desmoinesian-Missourian, and Artinskian Epochs. During these times maximum water temperatures of
42° to 56°C are well above the thermal threshold of protein denaturation. This process, which is lethal to most higher organisms,
demands an adjustment in oxygen of -2.5%. for samples older than Missourian, and of -1.250%. for samples spanning the Missourian-Artinskian
interval. With these adjustments and salinity considerations made prior to calculations, water temperatures become reasonable
for the Late Paleozoic epeiric, tropical seas of North America. 相似文献
980.
Henning Hintzsche Christian Jastrow Thomas Kleine-Ostmann Uwe K?rst Thorsten Schrader Helga Stopper 《PloS one》2012,7(9)
Terahertz electromagnetic fields are non-ionizing electromagnetic fields in the frequency range from 0.1 to 10 THz. Potential applications of these electromagnetic fields include the whole body scanners, which currently apply millimeter waves just below the terahertz range, but future scanners will use higher frequencies in the terahertz range. These and other applications will bring along human exposure to these fields. Up to now, only a limited number of investigations on biological effects of terahertz electromagnetic fields have been performed. Therefore, research is strongly needed to enable reliable risk assessment.Cells were exposed for 2 h, 8 h, and 24 h with different power intensities ranging from 0.04 mW/cm2 to 2 mW/cm2, representing levels below, at, and above current safety limits. Genomic damage on the chromosomal level was measured as micronucleus formation. DNA strand breaks and alkali-labile sites were quantified with the comet assay. No DNA strand breaks or alkali-labile sites were observed as a consequence of exposure to terahertz electromagnetic fields in the comet assay. The fields did not cause chromosomal damage in the form of micronucleus induction. 相似文献