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1.
The autotroph Methanococcus maripaludis contained high levels of acetate-coenzyme A ligase, pyruvate synthase, pyruvate, water dikinase, pyruvate carboxylase, and the enzymes of the incomplete reductive tricarboxylic acid cycle. Phosphoenolpyruvate carboxykinase, citrate synthase, and isocitrate dehydrogenase were not detected. In contrast, the heterotroph Methanococcus sp. strain A3 contained acetate kinase, and acetate coenzyme A ligase was virtually absent. 相似文献
2.
Sequence and translation of the murine coronavirus 5''-end genomic RNA reveals the N-terminal structure of the putative RNA polymerase. 总被引:20,自引:15,他引:5
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A 28-kilodalton protein has been suggested to be the amino-terminal protein cleavage product of the putative coronavirus RNA polymerase (gene A) (M.R. Denison and S. Perlman, Virology 157:565-568, 1987). To elucidate the structure and mechanism of synthesis of this protein, the nucleotide sequence of the 5' 2.0 kilobases of the coronavirus mouse hepatitis virus strain JHM genome was determined. This sequence contains a single, long open reading frame and predicts a highly basic amino-terminal region. Cell-free translation of RNAs transcribed in vitro from DNAs containing gene A sequences in pT7 vectors yielded proteins initiated from the 5'-most optimal initiation codon at position 215 from the 5' end of the genome. The sequence preceding this initiation codon predicts the presence of a stable hairpin loop structure. The presence of an RNA secondary structure at the 5' end of the RNA genome is supported by the observation that gene A sequences were more efficiently translated in vitro when upstream noncoding sequences were removed. By comparing the translation products of virion genomic RNA and in vitro transcribed RNAs, we established that our clones encompassing the 5'-end mouse hepatitis virus genomic RNA encode the 28-kilodalton N-terminal cleavage product of the gene A protein. Possible cleavage sites for this protein are proposed. 相似文献
3.
Plasma lipid and lipoprotein concentrations were determined in 30 males without diabetes or symptomatic coronary artery disease (CAD), and compared to the values in age-matched and weight-matched males (n = 55) with non-insulin-dependent diabetes mellitus (NIDDM). Patients with NIDDM were further subdivided into those with (n = 30) and without (n =25) CAD. Mean (+/- SEM) plasma triglyceride concentrations were significantly increased (P less than 0.001) over control values (96 +/- 5 mg/dl) in patients with NIDDM, whether with (172 +/- 14 mg/dl) or without documented CAD (164 +/- 25 mg/dl). Plasma cholesterol concentrations were also higher (P less than 0.001) than normal (168 +/- 5 mg/dl) in both groups of patients with NIDDM (201 +/- 11 and 199 +/- 7 mg/dl, respectively, in patients with and without evidence of CAD). Plasma LDL-cholesterol concentrations were also greater (P less than 0.001) than normal (104 +/- 4 mg/dl) in patients with NIDDM, but were again similar in the group of diabetics (120 +/- 9 vs 128 +/- 6 mg/dl). However, plasma HDL-cholesterol concentrations were only reduced below control values in diabetes patients with CAD (30 +/- 1 mg/dl), whereas patients with NIDDM and no subjective evidence of CAD had HDL-cholesterol concentrations (37 +/- 3 mg/dl) which were similar to normal values (38 +/- 2 mg/dl). As a result, the ratio of LDL-cholesterol to HDL-cholesterol was highest in patients with NIDDM and CAD (4.2 +/- 0.3), lowest in the control population (2.8 +/- 0.2), and intermediate in those patients with NIDDM without subjective or objective evidence of CAD (3.6 +/- 0.3).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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Carbon Assimilation and Leaf Water Status in Sugar Beet Leaves during a Simulated Natural Light Regimen
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Carbon assimilation and leaf water status were studied in sugar beet (Beta vulgaris L., Klein E-type multigerm) leaves during a light period in which illumination either increased rapidly to full irradiance or changed gradually in a sinusoidal manner as generally occurs during a natural day. A light regimen that simulated the light of a natural day was produced by adjusting irradiance with a neutral-density filter under the control of a computer. Under this light regimen, photosynthesis, transpiration, and stomatal conductance followed the irradiance pattern very closely and ribulose bisphosphate carboxylase was nearly fully activated. When illumination was increased rapidly at the beginning of a light period, transpiration also increased quickly, causing leaves to wilt to some extent. The activation state of ribulose bisphosphate carboxylase increased to only 52%, but ribulose bisphosphate level was nearly twice as high as during the simulated natural day. In spite of the differences in activation state and ribulose bisphosphate levels, photosynthesis rates were very similar under both regimens. Nevertheless, differences in parameters between leaves under the two irradiance regimens can affect how a plant responds to internal or external factors, and therefore, the rate at which irradiance increases at the beginning of a light period is an important consideration when interpreting data. 相似文献
7.
The cyclophilin homolog ninaA is a tissue-specific integral membrane protein required for the proper synthesis of a subset of Drosophila rhodopsins. 总被引:26,自引:0,他引:26
Mutations in the Drosophila ninaA gene cause dramatic reductions in rhodopsin levels, leading to impaired visual function. The ninaA protein is a homolog of peptidyl-prolyl cis-trans isomerases. We find that ninaA is unique among this family of proteins in that it is an integral membrane protein, and it is expressed in a cell type-specific manner. We have used transgenic animals misexpressing different rhodopsins in the major class of photoreceptor cells to demonstrate that ninaA is required for normal function by two homologous rhodopsins, but not by a less conserved member of the Drosophila rhodopsin gene family. This demonstrates in vivo substrate specificity in a cyclophilin-like molecule. We also show that vertebrate retina contains a ninaA-related protein and that ninaA is a member of a gene family in Drosophila. These data offer insights into the in vivo role of this important family of proteins. 相似文献
8.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
9.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
10.