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1.
An ATP-Sensitive K+ Current that Regulates Progression Through Early G1 Phase of the Cell Cycle in MCF-7 Human Breast Cancer Cells 总被引:4,自引:0,他引:4
Whole-cell recordings were used to identify in MCF-7 human breast cancer cells the ion current(s) required for progression
through G1 phase of the cell cycle. Macroscopic current-voltage curves were fitted by the sum of three currents, including
linear hyperpolarized, linear depolarized and outwardly rectifying currents. Both linear currents, but not the outwardly rectifying
current, were increased by 1 μm intracellular Ca2+ and blocked by 2 mm intracellular ATP. When tested at concentrations previously shown to inhibit proliferation by 50%, linogliride, glibenclamide
and quinidine inhibited the linear hyperpolarized current, and quinidine and linogliride inhibited the linear depolarized
current; none of these agents affected the outwardly rectifying current. In contrast, tetraethylammonium completely inhibited
the outwardly rectifying current, but did not inhibit either linear current. Changing the bath solution to symmetric K+ shifted the reversal potential of the linear hyperpolarized current from near the K+ equilibrium potential (−84 mV) to −4 mV. Arrest of the cell cycle in early G1 by quinidine was associated with significantly
smaller linear hyperpolarized currents, without a change in the linear depolarized or outwardly rectifying currents, but this
reduction was not observed with arrest by lovastatin at a site ≈6 hr later in G1. The linear hyperpolarized current was significantly
larger in ras-transformed than in untransformed cells. We conclude that the linear hyperpolarized current is an ATP-sensitive K+ current required for progression of MCF-7 cells through G1 phase.
Received: 22 January 1999/Revised: 11 May 1999 相似文献
2.
Tobias Gerlach Dennis Sprenger Nico K. Michiels 《Proceedings. Biological sciences / The Royal Society》2014,281(1787)
Fluorescence enables the display of wavelengths that are absent in the natural environment, offering the potential to generate conspicuous colour contrasts. The marine fairy wrasse Cirrhilabrus solorensis displays prominent fluorescence in the deep red range (650–700 nm). This is remarkable because marine fishes are generally assumed to have poor sensitivity in this part of the visual spectrum. Here, we investigated whether C. solorensis males can perceive the fluorescence featured in this species by testing whether the presence or absence of red fluorescence affects male–male interactions under exclusive blue illumination. Given that males respond aggressively towards mirror-image stimuli, we quantified agonistic behaviour against mirrors covered with filters that did or did not absorb long (i.e. red) wavelengths. Males showed significantly fewer agonistic responses when their fluorescent signal was masked, independent of brightness differences. Our results unequivocally show that C. solorensis can see its deep red fluorescent coloration and that this pattern affects male–male interactions. This is the first study to demonstrate that deep red fluorescent body coloration can be perceived and has behavioural significance in a reef fish. 相似文献
3.
We describe and compare inward and outward whole-cell K+ currents across the plasma membrane surrounding guard-cell protoplasts from the dicotyledon, Vicia faba, and the graminaceous monocotyledon, Zea mays. Macrosopic whole-cell current is considered in terms of microscopic single-channel activity, which involves discrete steps
between conducting (open) and nonconducting (closed) states of the channel protein. Kinetic equations are used to model the
number of open and closed states for channels conducting K+ influx (K(in)) and K+ efflux (K(out)) in the two species, and to calculate the rate at which open-closed transitions occur. The opening and closure
of K(in) channels in both Vicia and Zea follow single-exponential timecourses, indicating that K(in)-channel proteins in each species simply fluctuate between one
open and one closed state. In both species, opening of K(in) channels is voltage-independent, but closure of K(in) channels
is faster at more positive membrane potentials. In response to identical voltage stimuli, K(in) channels in Zea open and close approximately three times as fast as in Vicia. In contrast to K(in), K(out) channels in Zea open and close more slowly than in Vicia. The closure of K(out) channels follows a single-exponential timecourse in each species, indicating one open state. The kinetics
of K(out)-channel opening are more complicated and indicate the presence of at least two (Vicia) or three (Zea) closed states.
The authors thank Professor N.A. Walker and Dr. D.R. Laver for the use of laboratory equipment, for helpful discussion and
for provision of the program, GETHH. Thanks also to Dr. R.J. Ritchie for assistance with statistical analyses and to Ms. Janet
Sherwood for maintenance of Vicia and Zea plants. This work was supported by grants from the National Science Foundation (DCB-89-04041) and the McKnight Foundation
(S.M.A) and by a Charles Gilbert Heydon Travelling Fellowship (K.F-G). 相似文献
4.
Inward rectifier potassium (Kir) channels play essential roles in regulating diverse physiological processes. Although Kir channels are encoded in mosquito genomes, their functions remain largely unknown. In this study, we identified the members of the Anopheles gambiae Kir gene family and began to investigate their function. Notably, we sequenced the A. gambiae Kir1 (AgKir1) gene and showed that it encodes all the canonical features of a Kir channel: an ion pore that is composed of a pore helix and a selectivity filter, two transmembrane domains that flank the ion pore, and the so-called G-loop. Heterologous expression of AgKir1 in Xenopus oocytes revealed that this gene encodes a functional, barium-sensitive Kir channel. Quantitative RT-PCR experiments then showed that relative AgKir1 mRNA levels are highest in the pupal stage, and that AgKir1 mRNA is enriched in the adult ovaries. Gene silencing of AgKir1 by RNA interference did not affect the survival of female mosquitoes following a blood meal, but decreased their egg output. These data provide evidence for a new role of Kir channels in mosquito fecundity, and further validates them as promising molecular targets for the development of a new class of mosquitocides to be used in vector control. 相似文献
5.
p64 is a protein identified as a chloride channel by biochemical purification from kidney microsomes. We expressed p64 in
HeLa cells using a recombinant vaccinia virus/T7 RNA polymerase driven system. Total cell membranes were prepared from infected/transfected
cells and fused to a planar lipid bilayer. A novel chloride channel activity was found in cells expressing p64 and not in
control cells. The p64-associated activity shows strong anion over cation selectivity. Single channels show prominent outward
rectification with single channel conductance at positive potentials of 42 pS. The chloride channel activity is activated
by treatment of the membranes with alkaline phosphatase and inhibited by DNDS and by TS-TM calix(4)arene. Whole membrane anion
permeability was determined by a chloride efflux assay, revealing that membranes from cells expressing p64 showed a small
but highly significant increase in chloride permeability, consistent with expression of a novel chloride channel activity.
Received: 17 November 1997/Revised: 9 February 1998 相似文献
6.
A. V. Kireyko I. A. Veselova T. N. Shekhovtsova 《Russian Journal of Bioorganic Chemistry》2006,32(1):71-77
Peroxidase oxidation of o-dianisidine, 3,3′,5,5′-tetramethylbenzidine, and o-phenylenediamine in the presence of sodium dodecyl sulfate (SDS), an anionic surfactant, was spectrophotometrically studied. It was found that 0.1–100 mM SDS concentrations stabilize intermediates formed in the peroxidase oxidation of these substrates. The cause of the stabilization is an electrostatic interaction between positively charged intermediates and negatively charged surfactant. 相似文献
7.
Monoclonal antibodies against chick embryonic beta-galactoside-binding lectin were obtained. One of the monoclonal antibodies was ineffective in Western blotting and seemed to be unable to bind the SDS-denatured lectin. When the native lectin was dotted on a nitrocellulose filter and subjected to denaturation by treatment with SDS, urea or heat, binding of this antibody no longer occurred, though other monoclonal antibodies bound normally. This antibody seems to have been raised against an epitope which is destroyed upon denaturation. 相似文献
8.
Malou Philips Anne-Grethe Juul Sixtus Thorsen 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,802(1):99-110
Serum-free conditioned media and cell extracts from cultured human umbilical vein endothelial cells were analyzed for plasminogen activator by SDS-polyacrylamide gel electrophoresis and enzymography on fibrin-indicator gels. Active bands of free and complexed tissue-type plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-PA) were identified by the incorporation of specific antibodies against, respectively, t-PA or u-PA in the indicator gel. The endothelial cells predominantly released a high-molecular-weight t-PA (95000–135000). This t-PA form was converted to Mr-72000 t-PA by 1.5 M NH4OH/39 mM SDS. A component with high affinity for both t-PA and u-PA could be demonstrated in serum-free conditioned medium and endothelial cell extract. The complex between this component and Mr-72000 t-PA comigrated with high-molecular-weight t-PA. From the increase in Mr of t-PA or u-PA upon complex formation, the Mr of the endothelial cell component was estimated to be 50000–70000. The reaction between t-PA or u-PA and the plasminogen activator-binding component was blocked by 5 mM p-aminobenzamidine, while the complexes, once formed, could be cleaved by 1.5 M NH4OH/39 mM SDS. These observations indicated that the active center of plasminogen activator was involed in the complex formation. It was further noted that serum-free conditioned medium of endothelial cell extract inhibited plasminogen activator activity when assayed by the fibrin-plate method. Evidence is provided that the plasminogen activator-binding component was different from a number of the known plasma serine proteinase inhibitors, the placenta inhibitor and the fibroblast surface protein, proteinase-nexin. We conclude that cultured endothelial cells produce a rapid inhibitor of u-PA and t-PA as well as a t-PA-inhibitor complex. 相似文献
9.
Yusuke Nakamura Michio Ogawa Takahiro Nishide Mitsuru Emi Goro Kosaki Seiichi Himeno Kenichi Matsubara 《Gene》1984,28(2):263-270
The nucleotide sequences of the cloned human salivary and pancreatic α-amylase cDNAs correspond to the continuous mRNA sequences of 1768 and 1566 nucleotides, respectively. These include all of the amino acid coding regions. Salivary cDNA contains 200 bp in the 5′-noncoding region and 32 in the 3′-noncoding region. Pancreatic cDNA contains 3 and 27 bp of 5′- and 3′-noncoding regions, respectively. The nucleotide sequence humology of the two cDNAs is 96% in the coding region, and the predicted amino acid sequences are 94% homologous.Comparison of the sequences of human α-amylase cDNAs with those previously obtained for mouse α-amylase genes (Hagenbuchle et al., 1980; Schibler et al., 1982) showed the possibility of gene conversion between the two genes of human α-amylase. 相似文献
10.
The rhodopsin preparation obtained by the method of ammonium sulfate fractionation contained 3–6 mol phospholipid and about 18 mol cholate per mol rhodopsin. The purified rhodopsin had 74% helical structure and showed a visible CD spectrum different from that of rhodopsin in the membrane. The rhodopsin was stable below but denatured gradually above 20°C. The lifetime of metarhodopsin I was long in this preparation. Regeneration capacity was low and only 30% of the original rhodopsin was regenerable by addition of 11-cis-retinal after bleaching.50 mol of phosphatidylcholine were maximally bound to 1 mol rhodopsin when the purified rhodopsin was mixed with phosphatidylcholine in 0.5% cholate. The rhodopsin recombined with lipid had properties similar to those of the original rhodopsin in the membrane. Exchange of cholate for other detergents was easily performed by dialysis. The rhodopsin preparation in which cholate was exchanged for digitonin gave almost the same CD, thermal stability and regenerability as those of a native rhodopsin in the membrane but metarhodopsin I still retained its long lifetime. 相似文献