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981.
Rolf Altenburger Sibylle Abarzua Rainer Callies L. Horst Grimme Adalbert Mayer Dieter Leibfritz 《Archives of microbiology》1991,156(6):471-476
Cultures of the cyanobacterium Microcystis firma show rhythmic uptake and release of ammonia under conditions of carbon limitation. The massive removal of ammonia from the medium during the first light phase has little impact on the intracellular pH: a pH shift of less than 0.2 U towards the alkaline can be measured by in vivo 31P NMR. Furthermore, the energy status of the cells remains regulated. In vivo 15N NMR of M. firma, cultivated either with labelled nitrate or ammonia as the sole nitrogen source, reveals only gradual differences in the pool of free amino acids. Additionally both cultivation types show -aminobutyric acid, acid amides and yet unassigned secondary metabolites as nitrogen storing compounds. Investigating the incorporation of nitrogen under carbon limitation, however, only the amide nitrogen of glutamine is found permanently labelled in situ. While transamination reactions are blocked, nitrate reduction to ammonia can still proceed. Cation exchange processes in the cell wall are considered regarding the ammonia disappearance in the first phase, and the control of ammonia uptake is discussed with respect to the avoidance of intracellular toxification.Abbreviations GABA
-aminobutyric acid
- GOGAT
glutamate synthase
- GS
glutamine synthetase
- MDP
methylene diphosphonate
- MOPSO
3-(N-morpholino)-2-hydroxy-propanesulfonic acid
- NDPS
nucieoside diphosphosugars
- NOE
nuclear Overhauser effect
- NMR
nuclear magnetic resonance
For convenience, the term ammonia is used throughout to denote ammonia or ammonium ion when there is no good evidence as to which chemical species is involved 相似文献
982.
When a new strain of Pseudomonas aeruginosa was grown aerobically and then transferred to anaerobic conditions, cells reduced NO
3
–
quantitatively to NO
2
–
in NO
3
–
-respiration. In the absence of nitrate, NO
2
–
was immediately reduced to NO or N2O but not to N2 indicating that NO
2
–
-reductase but not N2O-reductase was active. The formation of the products NO or N2O depended on the pH in the medium and the concentration of NO
2
–
present. When P. aeruginosa was grown anaerobically for at least three davs N2O-reductase was also active. Such cells reduced NO to N2 via N2O. The new strain generated a H+-gradient and grew by reducing N2O to N2 but not by converting NO to N2O. For comparison, Azospirillum brasilense Sp7 showed the same pattern of NO-reduction. In contrast, Paracoccus denitrificans formed 3.5 H+/NO during the reduction of NO to N2O in oxidant pulse experiments but could not grow in the presence of NO. Thus the NO-reduction pattern in P. denitrificans on one side and P. aeruginosa and A. brasilense on the other was very different. The mechanistic implications of such differences are discussed. 相似文献
983.
Several quinolizidine alkaloids, including various angelate esters, are known from the genus Pearsonia. In a detailed variation study which included 98 samples from nine of the 11 species, large qualitative and quantitative differences were recorded. The observed variation is ascribed to the following: 1, species (the alkaloids of some species and subspecies are diagnostically different); 2, provenance (various populations of the same species may have unique combinations of alkaloids); 3, developmental stage (in P. cajanifolia there is a marked decreased in esterification towards the end of the growing season); 4, plant parts extracted (seeds, for example, have high concentrations of hydroxylated lupanine-type alkaloids and only small amounts of esters). These results highlight some of the problems associated with the use of alkaloids as taxonomic characters. 相似文献
984.
Butterfly migration from and to peninsular Florida 总被引:1,自引:0,他引:1
THOMAS J. WALKER 《Ecological Entomology》1991,16(2):241-252
Abstract.
- 1 Migrating butterflies were monitored with traps for 10 years at a site in north peninsular Florida, to determine seasonal and annual variation in numbers and directions of flight.
- 2 In the spring, 81–96% of the principal migrants, Phoebis sennae (L.), Agraulis vanillae (L.), Precis coenia (Hübner) and Urbanus proteits (L.), flew northward; in the autumn, 86–95% flew southward.
- 3 Estimated mean net numbers of these four species flying northward in spring across each ENE-WSW metre were 3, 6, 69 and <1 respectively; numbers flying southward in autumn were 222, 413, 37 and 146.
- 4 During a 5-year period, the ratio of highest to lowest seasonal migration for a species did not exceed 9.3.
- 5 The average median date of spring migration was 27 March for P.sennae, 23 April for P.coenia, and 12 May for A.vanillae. The average median date of autumn migration was 2–5 October except for U.proteus, whose average date was 14 October.
- 6 The autumn migratory period, as measured by the duration of the middle half of migration, was about 2 weeks in P.coenia and about 4 weeks in the other three species.
- 7 Compared to previously reported butterfly migrations, the ones studied here were notably uniform in magnitude and regular in timing.
- 8 These and other data suggest that 4 million or more of these butterflies migrate northward from peninsular Florida almost every spring and that 40 million or more migrate southward to peninsular Florida almost every autumn.
985.
W. Dörr J. Kummermehr 《Virchows Archiv. B, Cell pathology including molecular pathology》1991,60(1):287-294
Epithelial proliferation in the ventral surface of mouse tongue follows a pronounced circadian rhythm with a peak in mitotic
activity at 10.00 a.m., preceded by a wave of DNA synthesis 8 h earlier. Nearly all cells (85%) pass through G2 and mitosis
immediately after the S-phase; they subsequently divide again, usually after 2 or 3 days, indicating cohorts of cells with
different G1-duration. The fraction of all nucleated cells comprised in one daily proliferation wave is about 20%, indicating
a turnover time of the nucleated cell compartment of about 5 days. Cytotoxic injury by a single radiation dose of 20 Gy causes
a steep decrease in cell counts, leading to complete denudation after 9–13 days. The difference between the latent period
before ulceration and the tissue turnover time is explained by a marked proliferative activity of the doomed cells. The mitotic
index increases steeply after day 1 to three times the control level, but most mitotic figures display gross abnormalities
such as multipolar spindles or chromosome clumping. As a consequence cells with abnormal or multiple nuclei appear in the
basal layers 3 days post irradiation and subsequently migrate to the upper layers. After denudation the epithelium rapidly
becomes restored, with a phase of transient hyperplasia on days 13–14. Normal architecture is regained by day 15. Over the
whole healing period the mitotic index remains at a high level, with most of the mitoses appearing histologically normal. 相似文献
986.
In hippocampal slices arachidonic acid released after NMDA post-synaptic receptor activation is thought to act as a retrograde trans-synaptic messenger which facilitates the pre-synaptic release of L-glutamate to be involved in the expression of long-term synaptic potentiation (LTP). We measured the mass amount of arachidonic acid released from hippocampal slices incubated under conditions which maintain the electrophysiological responsiveness of the slice. Melittin released arachidonic, oleic and docosahexaenoic acids by phospholipase A2 activation but not palmitic or stearic acids. Of greater interestl-glutamate, N-methyl-d-aspartate and incubation conditions known to induce LTP selectively and rapidly increased the release of archidonic acid in amounts over basal levels of 200–300 ng/mg protein. This is the first direct determination of the mass amount of arachidonic acid released following NMDA receptor activation in the hippocampus.Special issue dedicated to Dr. Louis Sokoloff. 相似文献
987.
Pharmacological and biochemical characteristics of the partially purified -aminobutyric acid (GABA)B receptor using baclofen affinity column chromatography have been examined. The Scatchard analysis of [3H]GABA binding to the purified GABAB receptor showed a linear relationship and the KD and Bmax values were 60 nM and 118 pmol/mg of protein, respectively. Although GTP and Mg2+ did not affect on the GABAB receptor binding, Ca2+ significantly increased [3H]GABA binding to the purified GABAB receptor in a dose-dependent manner and showed its maximum effect at 2 mM. The enhancement of the binding by Ca2+ was found to be due to the increase of Bmax by the Scatchard analysis. The treatments with pronase and trypsin significantly decreased the binding of [3H]GABA, but phospholipase A2 had no significant effect on the binding. In addition, treatment with glycosidases such as glycopeptidase A and -galactosidase significantly decreased the binding of [3H]GABA to the purified GABAB receptor. These results suggest that purification of the solubilized GABAB receptor by the affinity column chromatography may result in the functional uncoupling of GABAB receptor with GTP-binding protein. Furthermore, the present results suggest that cerebral GABAB receptor may be a glycoprotein and membrane phospholipids susceptible to phospholipase A2 treatment may not be involved in the exhibition of the binding activity.Special issue dedicated to Dr. Eugene Roberts. 相似文献
988.
The effects of a single does of LiCl (2.5 or 10 mEq/kg) on brain inositol and inositol-1-phosphate (Ins1P), intermediates of brain phosphoinositude (PI) turnover, were determinated in male Han: Wistar rats. There was a remarkable, 36–58 fold elevation of brain Li+ as the single does of LiCl was increased 4-fold. Moreover, the accumulation of brain lithium was slow during repeated administration of LiCl. Brain lithium did not correlate with changes in brain PI turnover either after a single or repeated doses. Thus, after a single does of LiCl the increases in brain Ins1P were much less than the decreases in brain inositol. Also, brain inositol was significantly decreased only with the high dose of LiCl whereas brain Ins1P accumulation was more prominent with the lower dose. Moreover, repeated daily doses of LiCl only transiently increased brain Ins1P at 1 and 7 d whereas inositol remained at control levels throughout the 14 d observation period. Lithium probably caused the transient decrease in brain inositol by inhibiting several enzymes, in addition to the inhibition of myo-inositol mono-phosphates, in the PI cycle. Moreover, a slow dampening down of PI turnover by lithium, possible via an inhibitory action on G-protein-coupling, may also explain the present findings. 相似文献
989.
990.