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1.
Monica Driscoll 《Developmental neurobiology》1992,23(9):1327-1351
In C. elegans, cell death can be readily studied at the cellular, genetic, and molecular levels. Two types of death have been characterized in this nematode: (1) programmed cell death, which occurs as a normal component in development; and (2) pathological cell death which occurs aberrantly as a consequence of mutation. Analysis of mutations that disrupt programmed cell death in various ways has defined a genetic pathway for programmed cell death which includes genes that perform such functions as the determination of which cells die, the execution of cell death, the engulfment of cell corpses, and the digestion of DNA from dead cells. Molecular analysis is providing insightinto the nature of the molecules that function in these aspects of programmed cell death. Characterization of some genes that mutate to induce abnormal cell death has defined a novel gene family called degenerins that encode putative membrane proteins. Dominant alleles of at least two degenerin genes, mec-4 and deg-1, can cause cellular swelling and late onset neurodegeneration of specific groups of cells. © 1992 John Wiley & Sons, Inc. 相似文献
2.
3.
Manganese cycling in an acidic Adirondack lake 总被引:4,自引:4,他引:0
There is considerable interest in the chemistry of Mn in acidic waters because of its role in the generation of acid neutralizing capacity during reduction processes, as an adsorbent in element cycling, and as a potential toxicant to aquatic organisms. Temporal and spatial variations in the concentration of Mn were evident in acidic Dart's Lake (1.0–2.3 mol l–1), located in the Adirondack Region of New York. Seasonal changes in pH and dissolved oxygen concentration had subtle effects on the chemistry and transport of Mn. Despite oversaturation with respect to the solubility of manganite during periods of stratification, vertical deposition of Mn was minimal. The conservative nature of Mn appears to be due to the acidic conditions in Dart's Lake. 相似文献
4.
Robert A. Goldstein Steven A. Gherini Charles T. Driscoll Richard April Carl L. Schofield Carl W. Chen 《Biogeochemistry》1987,3(1-3):5-20
An integrated analysis of a terrestrial-aquatic ecosystem, the North Branch of the Moose River in the Adirondack region of New York, was conducted. This basin contains a large number of interconnected surface waters that exhibit marked gradients in pH and acid neutralizing capacity (ANC). As a result, the basin has been the focus of research activity, including the Regional Integrated Lake-Watershed Acidification Study (RILWAS). The objective of the current analysis was to use the North Branch of the Moose River as a case study to:
- Evaluate processes regulating the acid-base chemistry of surface waters.
- To assess the effects of surface water acidification on fish populations.
5.
Concentration and flux of solutes from snow and forest floor during snowmelt in the West-Central Adirondack region of New York 总被引:7,自引:7,他引:0
Decreases in pH and increases in the concentration of Al and NO
3
–
have been observed in surface waters draining acid-sensitive regions in the northeastern U.S. during spring snowmelt. To assess the source of this acidity, we evaluated solute concentrations in snowpack, and in meltwater collected from snow and forest floor lysimeters in the west-central Adirondack Mountains of New York during the spring snowmelt period, 29 March through 15 April 1984.During the initial phase of snowmelt, ions were preferentially leached from the snowpack resulting in elevated concentrations in snowmelt water (e.g. H+ = 140 eq.l–1; NO
4
2–
= 123 eq.l–1; SO
3
–
= 160 eq.l–1). Solute concentrations decreased dramatically within a few days of the initial melt (< 50 eq.l–1). The concentrations of SO
4
2–
and NO
3
–
in snowpack and snowmelt water were similar, whereas NO–
3 in the forest floor leachate was at least two times the concentration of SO
4
2–
.Study results suggest that the forest floor was a sink for snowmelt inputs of alkalinity, and a net source of H+, NO
3
–
, dissolved organic carbon, K+ and Al inputs to the mineral soil. The forest floor was relatively conservative with respect to snowmelt inputs of Ca2+, SO
4
2–
and Cl–. These results indicate that mineralization of N, followed by nitrification in the forest floor may be an important process contributing to elevated concentrations of H+ and NO
3
–
in streams during the snowmelt period. 相似文献
6.
Barbara R. Grubb Suzanne M. Driscoll P. J. Bentley 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(2):181-186
In vitro measurements were made of transmural potential difference (PD), short-circuit current (Isc), resistance and unidirectional fluxes of 22Na and 36Cl across the duodenum, jejunum, ileum and colon of normal sodium-replete domestic fowl (Gallus domesticus). The PD ranged from about 1 mV across the duodenum to 8 mV across the colon while the Isc was, respectively, 2.8 and 64 microA X cm-2. The jejunum and ileum exhibited values between these extremes. Unidirectional fluxes (under short-circuit conditions) of Na and Cl were lowest across the duodenum where there was no evidence of active transport of these ions. Unidirectional fluxes of Na and Cl were less across the jejunum than across the ileum or colon. A net active transport of Na (but not Cl) was observed in the ileum (= 106% of the Isc) and colon (= 50% of Isc). The possible physiological significance of these observations in the domestic fowl are discussed and are compared to that of a mammal, the rabbit. 相似文献
7.
Locus determining the human sperm-specific lactate dehydrogenase, LDHC, is syntenic with LDHA 总被引:5,自引:0,他引:5
Y H Edwards S Povey K M LeVan C E Driscoll J L Millan E Goldberg 《Developmental genetics》1987,8(4):219-232
From the data presented in this report, the human LDHC gene locus is assigned to chromosome 11. Three genes determine lactate dehydrogenase (LDH) in man. LDHA and LDHB are expressed in most somatic tissues, while expression of LDHC is confined to the germinal epithelium of the testes. A human LDHC cDNA clone was used as a probe to analyze genomic DNA from rodent/human somatic cell hybrids. The pattern of bands with LDHC hybridization is easily distinguished from the pattern detected by LDHA hybridization, and the LDHC probe is specific for testis mRNA. The structural gene LDHA has been previously assigned to human chromosome 11, while LDHB maps to chromosome 12. Studies of pigeon LDH have shown tight linkage between LDHB and LDHC leading to the expectation that these genes would be syntenic in man. However, the data presented in this paper show conclusively that LDHC is syntenic with LDHA on human chromosome 11. The terminology for LDH genes LDHA, LDHB, and LDHC is equivalent to Ldh1, Ldh2, and Ldh3, respectively. 相似文献
8.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
相似文献
9.
Solvent and solvent proton dependent steps involved in the mechanism of the enzyme galactose oxidase have been examined. The deuterium kinetic solvent isotope effect (KSIE) on the velocity of the galactose oxidase catalyzed oxidation of methyl beta-galactopyranoside by O2 was measured. Examination of the thermodynamic activation parameters for the reaction indicated that the isotope effect was attributable to a slightly less favorable delta H value, consistent with a KSIE on proton transfer. A detailed kinetic analysis was performed, examining the effect of D2O on the rate of reaction over the pH range 4.8-8.0. Both pL-rate profiles exhibited bell-shaped curves. Substitution of D2O as solvent shifted the pKes values for the enzymic central complex: pKes1 from 6.30 to 6.80 and pKes2 from 7.16 to 7.35. Analysis of the observed shifts in dissociation constants was performed with regard to potential hydrogenic sites. pKes1 can be attributed to a histidine imidazole, while pKes2 is tentatively assigned to a Cu2+-bound water molecule. A proton inventory was performed (KSIE = +1.55); the plot of kcat vs. mole fraction D2O was linear, indicating the existence of a single solvent-derived proton involved in a galactose oxidase rate-determining step (or steps). The pH dependence of CN- inhibition was also examined. The Ki-pH profile indicated that a group ionization, with pKa = 7.17, modulated CN- inhibition; Ki was at a minimum when this group was in the protonated state. The inhibition profile followed the alkaline limit of the pH-rate profile for the enzymic reaction, suggesting that the group displaced by CN- was also deprotonating above pH 7.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
10.