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81.
InRhizobium meliloti, the promoter P1 of thenif HDK operon, and also the promoter P2, have earlier been shown to be active in the bacteria present in alfalfa root nodules, but
not in the bacteria grown aerobically in culture. Here we have looked at the expression from P1 and P2 in two non-symbiotic
nitrogen-fixing bacteria,Azotobacter vinelandii andAzospirillum brasilense, using constructions in which the promoters are fused upstream of theβ-galactosidase gene. The promoter P1, but not P2, is active inA. vinelandii, while neither P1 nor P2 is active inAzospirillum brasilense. 相似文献
82.
Effect of Maternal Alcohol Consumption on the Lipid Composition of CNS in the Offspring 总被引:1,自引:0,他引:1
T. Lalitha Krishna Kumar C. V. Ramakrishnan S. D. Telang 《Journal of neurochemistry》1988,50(5):1346-1351
Maternal alcohol consumption at a level that does not affect calorie intake increases cholesterol concentration and content as well as incorporation of labeled glucose into cholesterol in the brain and spinal cord of newborn rat pups. Continued consumption of alcohol during lactation also affects the galactolipid concentration in the brain and spinal cord of pups at 21 days of age, and this increase seems mainly to be due to an increase in content of myelin lipids. Analysis of myelin shows that the concentration of phospholipids also increases in this fraction. The increase in incorporation of labeled glucose into these membrane lipids suggests an increase in the synthesis of these lipids, which prevents fluidization of the membrane by alcohol. That in the brainstem the increase in levels of cholesterol and galactolipids is higher than in other regions and that there is also an increase in content of sphingomyelin, phosphatidylcholine, and phosphatidylethanolamine suggest that the brainstem needs better protection against fluidization. 相似文献
83.
Glutamic acid decarboxylase (GAD), gamma-[3H]-aminobutyric acid [( 3H]GABA) high-affinity uptake into synaptosomes, and endogenous GABA content were measured in the rat striatum 2-3 weeks following 6-hydroxydopamine injection in the ipsilateral substantia nigra to destroy the nigrostriatal dopaminergic pathway and after kainic acid injection into the centromedial-parafascicular complex of the ipsilateral thalamus to lesion the thalamostriatal input. Both lesions resulted in apparent GAD increase concomitant with a decreased [3H]GABA uptake into striatal synaptosomes. GABA content was increased selectively following the dopaminergic lesion. Kinetic analysis of the uptake process for [3H]GABA showed selectively a decreased Vmax following the dopaminergic lesion; in animals with thalamic lesion, however, the change only concerned the Km, which showed a decreased affinity of the transport sites for [3H]GABA. Determination of Km and Vmax for GAD action on its substrate glutamic acid showed an increased affinity of GAD for glutamic acid in the case of the dopaminergic lesion without any change in Vmax, whereas the thalamic lesion resulted in GAD increase concomitant with a selective increase in Vmax. These data suggest that striatal GABA neurons are under the influence of nigrostriatal dopaminergic neurons which may reduce the GABA turnover, whereas the exact nature of the powerful control also revealed on these neurons following thalamic lesion remains to be determined. Both lesions induced adaptive neurochemical responses of striatal GABA neurons, possibly reflecting in the case of the dopaminergic deprivation an increased GABA turnover. 相似文献
84.
An L1210 cell line (JT-1), which can grow in medium supplemented with 1 nM folate, has been isolated. These cells exhibit a slower growth rate than folate-replete parental cells and have a lower ability to transport folate or methotrexate via the reduced folate transport system. Measurements at nanomolar concentrations of folate revealed that the adapted cells have acquired a high-affinity folate-binding protein. Binding to this component at 37 degrees C was rapid and reached a maximum value after 30 min which corresponded in amount to 0.23 +/- 0.3 pmol/mg protein, and excess unlabeled folate added 30 min subsequent to the [3H]folate led to a rapid release of the bound substrate. Radioactivity bound to or released from the cells after 30 min at 37 degrees C remained as unmetabolized folic acid. Binding was also rapid at 0 degrees C but uptake at the plateau was only one-half the value obtained at 37 degrees C. Half-maximal saturation of the binding component (KD) occurred at a folate concentration of 0.065 nM at pH 7.4, while the affinity for folate decreased 30-fold when the pH was reduced to 6.2 (KD = 2.0 nM). 5-Methyltetrahydrofolate was also bound by this component (Ki = 13 nM at pH 7.4) but with a much lower affinity than for folate, while progressively weaker interactions were observed with 5-formyltetrahydrofolate (Ki = 45 nM) and methotrexate (Ki = 325 nM). When the same adaptation procedure was performed with limiting amounts of 5-formyltetrahydrofolate, two additional cell lines, JT-2 and JT-3, were isolated which expressed elevated levels of the folate-binding protein. The binding activity of the latter cells was 0.46 and 1.4 pmol/mg protein, respectively. When the level of binding protein was compared in cells grown at different concentrations of folate, an increase in medium folate from 1 to 500 nM caused a sevenfold reduction in binding activity in the JT-3 cell line, while these same growth conditions had no effect on binding by the other cells. These results indicate that L1210 cells adapted to low concentrations of folate or 5-formyltetrahydrofolate contain elevated levels of a high-affinity binding protein and that this protein is able to mediate the intracellular accumulation of folate compounds. L1210 cells thus appear to have two potential uptake routes for folate compounds, the previously characterized anion-exchange system and a second route mediated by a high-affinity binding protein.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
85.
Synthesis of functional human immunodeficiency virus tat protein in baculovirus as determined by a cell-cell fusion assay. 总被引:6,自引:3,他引:3 下载免费PDF全文
The human immunodeficiency virus tat protein is a strong trans-activator of the expression of mRNAs originating from the viral long terminal repeat. We have expressed the first 72 amino acids (coding exon 1) of this protein in eucaryotic Spodoptera frugiperda SF9 cells by using a baculovirus vector, Autographa californica nuclear polyhedrosis virus. We show that the baculovirus vector stably produced the 72-amino-acid form of the tat protein but was unable to stably synthesize a larger 101-amino-acid full-length version of the same polypeptide. The 72-amino-acid tat protein, when introduced into mammalian fibroblasts by using a cell-cell fusion technique, functionally trans-activated the expression of the human immunodeficiency virus long terminal repeat. 相似文献
86.
87.
Effect of mutations at Met-88 and Met-90 on the biotination of Lys-89 of the apo 1.3S subunit of transcarboxylase 总被引:3,自引:0,他引:3
The apo 1.3S subunit of transcarboxylase contains the sequence Ala-87-Met-88-Lys-89-Met-90, and it is Lys-89 that is biotinated. This sequence is highly conserved in all the biotin enzymes that have been sequenced (with the exception of acetyl-CoA carboxylase from chicken liver, which has Val in place of Ala). The role of Met-88 and Met-90 in specifying Lys-89 for biotination by synthetase was examined by site-directed mutagenesis. Genes of the 1.3S subunit coding for Thr-88, Leu-88, or Leu-90 were generated by oligonucleotide-directed in vitro mutagenesis and expressed in Escherichia coli. The mutated apo 1.3S subunits were isolated and the biotination by homogeneous synthetase from Propionibacterium shermanii was compared with that of the apo wild-type subunit. The Vmax for the apo mutants was the same as that for the apo wild type, but when Leu was substituted for Met-88 or Met-90, the Km for the mutant was lower than that of the wild-type or mutant Thr-88. The activity of the synthetase of E. coli was determined by an in vivo assay. During the early log phase of growth, a smaller portion of mutants Thr-88 and Leu-90 was biotinated than with the wild-type or mutant Leu-88. When the cultures progressed to stationary phase, mutants and the wild type were biotinated to the same extent. The overall results show that Met-88 and Met-90 are not required for biotination of the apo 1.3S subunit by the synthetases. 相似文献
88.
Influence of the food plants ofHeliothis armigera (Hb.) on the degree of parasitism by exotic parasiteCotesia kazak Telenga (Hymenoptera: Braconidae) was studied in cages in the laboratory on 7 food plants such as cotton (Gossypium hirsutum L.), tomato (Lycopersicon esculentum Mill), okra [Abelmoschus esculentus (L.) Moench], Dolichos (dolichos lablab L.), pigeonpea [Cajanus cajan (L.) Millsp.], Cowpea (Vigna unquiculata (L.) and chickpea (Cicer arietium L.). To determine the preference of the parasite 2 test methods were employed. In single plant choice test cotton was most
preferred. Next in order of preference were tomato and okra. Dolichos, pigeonpea, cowpea and chickpea were least preferred.
In multiple choice test, however, cotton and okra were preferred followed by tomato. Parasites were seen visiting these plants
very frequently and high parasitism was recorded on these plants. Chick pea, pigeon pea, cowpea and Dolichos were the least
preferred food plants. There appears to be some difference in fecundity as affected by some food plants. Exposure on okra,
cotton and tomato resulted in higher cocoon production as compared to pigeonpea, Dolichos, cowpea and chickpea. There was,
however, no difference in sex-ratio and longevity of the progeny as affected by food plants. This exotic parasite should be
released first in crops such as cotton, okra and tomato on whichH. armigera is a very serious pest in India and elsewhere.
Contribution No. 140/86 of the Indian institute of Horticultural Research, Bangalore-560 089 相似文献
89.
The possibility of interaction of hepatocytes with the heparin binding domain of Fibronectin was examined. Rat hepatocytes
adhered to coverslips coated with the 33-kDa heparin binding fragment of the C-terminal region of plasma fibronectin. When
different concentrations of the heparin binding fragment were used to coat coverslips and used as substratum, cell attachment
showed saturation kinetics. Half the maximum attachment was observed at 30–40 min after seeding of cells. The cells became
flat after 2–3 h indicating that they spread on the heparin binding domain as they do on intact fibronectin. Among the different
glycosaminoglycans tested, maximum inhibition of attachment was observed for heparin. However it was not possible to completely
inhibit attachment even at high concentrations. These results indicate that hepatocytes interact with fibronectin not only
through the Arg-Gly-Asp-containing cell binding fragment, but also through the heparin binding domain of fibronectin and,
further, that there exist heparin-dependent and heparin-independent mechanisms of interaction of cells with the 33-kDa heparin
binding fragment of fibronectin 相似文献
90.
Mini-exon derived RNA is a small nuclear RNA of trypanosomatid protozoa such asLeishmania which donates its 5′-terminal 39 nucleotides to the 5’-ends of cellular messenger RNAs by trans-splicing. We have cloned
a mini-exon derived RNA gene fromLeishmania donovani and studied its organization and expression. About 200 copies of the gene per haploid genome are organized as a tandem repeat
on a single chromosome. The gene is transcribed as a 95-nucleotide RNA. The first 39 nucleotides of mini-exon derived RNA
is also found at the 5′-terminus of a cellular mRNA (Β-tubulin), thus confirming its identity. Sequence analysis of the gene
and its flanking regions showed that while classical RNA polymerase II promoter elements such as TATA and CAAT are absent
from the 5′-upstream region, intragenic sequence motifs resembling RNA polymerase III promoter elements are present. The implications
of this finding for mini-exon derived RNA expression are discussed. 相似文献