全文获取类型
收费全文 | 8563篇 |
免费 | 704篇 |
国内免费 | 6篇 |
出版年
2023年 | 63篇 |
2022年 | 85篇 |
2021年 | 135篇 |
2020年 | 105篇 |
2019年 | 124篇 |
2018年 | 167篇 |
2017年 | 186篇 |
2016年 | 278篇 |
2015年 | 378篇 |
2014年 | 515篇 |
2013年 | 687篇 |
2012年 | 678篇 |
2011年 | 649篇 |
2010年 | 496篇 |
2009年 | 391篇 |
2008年 | 424篇 |
2007年 | 421篇 |
2006年 | 405篇 |
2005年 | 376篇 |
2004年 | 354篇 |
2003年 | 343篇 |
2002年 | 326篇 |
2001年 | 86篇 |
2000年 | 67篇 |
1999年 | 72篇 |
1998年 | 93篇 |
1997年 | 72篇 |
1996年 | 84篇 |
1995年 | 63篇 |
1994年 | 79篇 |
1993年 | 80篇 |
1992年 | 92篇 |
1991年 | 61篇 |
1990年 | 62篇 |
1989年 | 48篇 |
1988年 | 48篇 |
1987年 | 38篇 |
1986年 | 24篇 |
1985年 | 43篇 |
1984年 | 52篇 |
1983年 | 43篇 |
1982年 | 42篇 |
1981年 | 50篇 |
1980年 | 38篇 |
1978年 | 36篇 |
1977年 | 29篇 |
1976年 | 26篇 |
1974年 | 31篇 |
1972年 | 31篇 |
1971年 | 26篇 |
排序方式: 共有9273条查询结果,搜索用时 31 毫秒
21.
Summary Bacterivory was detected by incorporation of 0.57 m diameter, fluorescent polystyrene beads and fluorescently labeled bacteria (FLB) in two cultured species of Cryptomonas (C. ovata and C. erosa), and a population of Cryptomonas sp in a humic, mesotrophic lake. Rates of ingestion and clearance were very low, and similar for the cultures and the in situ population. The in situ population incorporated 0.7–1.7 bacteria cell-1 h-1, thereby ingesting 0.3%–2.0% of the total bacterial numbers present in the water per day, and receiving less than 2% of its carbon content per day through bacterivory. Thus, bacterivory by Cryptomonas was quantitatively important neither as a sink for bacterial biomass, nor as a carbon source for the algal cells. Possibly, it served in the uptake of essential nutrients. 相似文献
22.
Bacterioplankton growth, grazing mortality and quantitative relationship to primary production in a humic and a clearwater lake 总被引:8,自引:0,他引:8
Bacterial growth and grazing mortality were estimated from Mayto October in two south Swedish oligotrophic lakes, one beinga clearwater lake (water colour 510 mg Pt l1 DOC2.93.4 mg l1, Secchi disk depth 5.09.4m) and the other a humic, brownwater lake (water colour 105165mg Pt l1, DOC 13.722.7mg l1, Secchi diskdepth 1.32.1 m). Specific rates of growth and grazingmortality were generally similar for both lakes. However, theabundance of bacteria was consistently 23 times higherin the water of the humic lake, suggesting that the total productionand consumption of bacterial cells were also higher than inthe dearwater lake. The ratio of bacterial secondary productionto primary production was higher in the humic lake than in theclearwater lake, indicating that the bacterioplankton of thehumic lake utilize allochthonous substrates, in addition tosubstrates originating from autochthonous primary production.Most of the bacterial loss in both lakes could be attributedto small protozoan grazers. This implies that allochthonousand autochthonous organic carbon fixed by bacterioplankton isless important in terms of carbon flow to higher trophic levelsthan would be expected if macrozooplankton were the dominantbacterivores, providing a more direct and efficient transferof carbon to larger organisms. 相似文献
23.
Ulrik Pedersen-Bjergaard Lars B geskov Nielsen Kai Jensen Lars Edvinsson Inger Jansen Jes Olesen 《Peptides》1989,10(6):1147-1152
Neurokinin A (NKA), substance P (SP) and the two peptides combined (SP + NKA) were injected intracutaneously on the forearm and into the temporal muscle of healthy volunteers. Pain intensity, cutaneous wheal and flare responses and tenderness of the temporal muscle were quantitated. SP but not NKA induced cutaneous pain. This relates the algesic effect of SP to the specific N-terminal amino acid sequence of the peptide, not shared by NKA. NKA, however, potentiated the algesic effect of SP as SP + NKA induced a significantly prolonged cutaneous pain sensation. Both peptides induced wheals, but only SP induced flare. These results confirm previous studies relating wheal formation to the identical C-terminal amino acid sequence of the two peptides and flare reaction to the N-terminal part of SP. Injections into the temporal muscle did not cause pain or tenderness. 相似文献
24.
25.
26.
The effects of , , and receptor-agonists on forskolin stimulated cyclic adenosine-3, 5-monophosphate (cAMP) formation were examined in astroglial enriched primary cultures from the cerebral cortex of newborn rats. Intracellular cAMP accumulation was quantified by radioimmunoassay. Morphine was used as a -receptor agonist, D-Ala-D-Leu-Enkephalin (DADLE) as a -receptor agonist and dynorphine 1–13 (Dyn) as a -receptor agonist. Basal cAMP levels were unaffected by either the opiate agonists or the antagonists used. In the presence of the cAMP stimulator forskolin, morphine had no significant effect on the cytoplasmic cAMP levels. DADLE caused a dose related inhibition of the forskolin stimulated cAMP accumulation. The effects of this receptor stimulation was blocked with the selective antagonist ICI 174.864. In the presence of Dyn, the forskolin stimulated cAMP accumulation was inhibited in a dose related manner. This receptor stimulation was blocked with the selective antagonist MR 2266. Co-administration of DADLE and Dyn resulted in a non additive inhibition of the forskolin stimulated accumulation of cAMP. These findings indicate that astroglial enriched cultures from the cerebral cortex of rats express and -receptors co-localized ont he same population of cells, and that these receptors are inhibitory coupled to adenylate cyclase. 相似文献
27.
Summary The protothyroid region in the endostyles of four species of tunicates was examined by means of autoradiography and cytochemistry, at both the light and electronmicroscopic levels. To reveal the primary binding site for iodine, autoradiography was carried out on endostylar tissue from animals that had been incubated with high activity 125I- over a short period of time. The specific iodine binding enzyme, a peroxidase, was traced by its reaction with DAB. In accordance with previous findings, the iodinebinding cells proved to be the same as those containing the peroxidase. There were also strong indications of a secondary uptake of iodinated compounds and subsequent release into the body fluid. Together with the ultrastructural features, the data provided strong evidence indicating that these cells constitute a protothyroid region, which partly functions as an endocrine organ, possibly homologous with the vertebrate thyroid gland. Since the number of zones varied between the species, the numeration of the protothyroid region also varied. However, in all the examined endostyles, the protothyroid region was seen to be situated dorsolaterally to the glandular regions of the endostyle concerned with food capture. 相似文献
28.
Linkage relationships in the bovine MHC region. High recombination frequency between class II subregions 总被引:2,自引:2,他引:0
Leif Andersson Anne Lundén Sunna Sigurdardottir Christopher J. Davies Lars Rask 《Immunogenetics》1988,27(4):273-280
Class II genes of the bovine major histocompatibility complex (MHC) have been investigated by Southern blot analysis using human DNA probes. Previous studies revealed the presence of bovine DO
, DQ
, DQ
, DR
and DR
genes, and restriction fragment length polymorphisms for each of these genes were documented. In the present study, the presence of three additional class II genes, designated DZ
, DY
, and DY
, are reported. DZ
was assumed to correspond to the human DZ
gene while the other two were designated DY because their relationship to human class II genes could not be firmly established. The linkage relationships among bovine class II genes and two additional loci, TCP1B and C4, were investigated by family segregation analysis and analysis of linkage disequilibrium. The results clearly indicated that all these loci belong to the same linkage group. This linkage group is divided into two subregions separated by a fairly high recombination frequency. One region includes the C4, DQ
, DQ
, DR
and DR
loci and the other one is composed of the DO
DY
, DY
, and TCPIB loci. No recombinant was observed within any of these subregions and there was a strong or fairly strong linkage disequilibrium between loci within groups. In contrast, as many as five recombinants among three different families were detected in the interval between these subregions giving a recombination frequency estimate of 0.17 ± 0.07. The fairly high recombination frequency observed between class 11 genes in cattle is strikingly different from the corresponding recombination estimates in man and mouse. The finding implies either a much larger molecular distance between some of the bovine class II genes or alternatively the presence of a recombinational hot spot in the bovine class II region. 相似文献
29.
Mustafa Özilgen 《Applied microbiology and biotechnology》1988,29(6):536-543
Summary Large amounts of data indicated that most of the metabolic processes of the acidogenic (acid producing) and the solventogenic (solvent producing) fermentations were regulated by product accumulation. A simple unstructured model simulated microbial growth, product formation and substrate utilization in six different fermentations, where five different microorganisms produced various combinations of ten different products. Specific growth rates of these microorganisms decreased proportionally with overall product accumulation. The products were excreted in non-growth associated pattern. Excretion of some of these products were inhibited by the overall product accumulation similarly as the microbial growth. A substrate consumption model which considered the biomass and individually all the products as separate substrate sinks simulated the data satisfactorily. 相似文献
30.