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971.
Food limitation was tested in the laboratory by individual growth and reproduction of two cladoceran species, Ceriodaphnia richardi and Daphnia gessneri, from the shallow tropical Brazilian Lake Monte Alegre. The cladocerans were fed cultivated green alga Scenedesmus spinosus in concentrations of 0.20, 0.10, 0.05, and 0.025 mg C l−1. Higher biomass and growth rates occurred in the two highest-food concentrations; the two lowest ones negatively affected
clutch size and first reproduction. The threshold food concentration is lower than 0.025 mg C l−1 and the incipient limiting level is a value between 0.10 and 0.20 mg C l−1. The largest species, D. gessneri, was more sensitive to low food concentrations. The effects of low and high temperatures (19 and 27°C) were evaluated by
life table experiments with three cladocerans from the lake—Daphnia ambigua, D. gessneri, and Moina micrura—with no food limitation (1 mg C l−1 of S. spinosus). Higher population growth rates for the three species were found at 27°C; better performance in most life table parameters
was observed for the former two species at the highest temperature, D. gessneri being the most sensitive to the lowest temperature. There are indications that temperature is an important abiotic factor
that constrains populations of cladocerans for a short period in winter in the lake, when temperature decreases to 18–19°C.
However, its influence cannot be separated from a biotic factor such as food, whose effect is stronger in the cool season,
when concentrations are lower and contribution of inedible algae is relatively higher. 相似文献
972.
Hyaluronic acid: a natural biopolymer with a broad range of biomedical and industrial applications 总被引:2,自引:0,他引:2
Hyaluronic acid (hyaluronan, HA) is a linear polysaccharide formed from disaccharide units containing N-acetyl-d-glucosamine and glucuronic acid. It has a high molecular mass, usually in the order of millions of Daltons, and interesting
viscoelastic properties influenced by its polymeric and polyelectrolyte characteristics. HA is present in almost all biological
fluids and tissues. In clinical medicine, it is used as a diagnostic marker for many diseases including cancer, rheumatoid
arthritis and liver pathologies, as well as for supplementation of impaired synovial fluid in arthritic patients by means
of intra-articular injections. It is also used in certain ophthalmological and otological surgeries and cosmetic regeneration
and reconstruction of soft tissue. Herein we present an overview of the occurrence and physiological properties of HA, as
well as of the recent advances in production biotechnology and preparation of the HA-based materials for medical application. 相似文献
973.
Novel Rumen Bacterial Diversity in Two Geographically Separated Sub-Species of Reindeer 总被引:2,自引:0,他引:2
Svalbard reindeer (Rangifer tarandus platyrhynchus) live under austere nutritional conditions on the high-arctic archipelago of Svalbard, while semi-domesticated Norwegian
reindeer (R. tarandus tarandus) migrate between lush coastal summer pastures and inland winter pastures with lichens on mainland Norway. Svalbard reindeer
are known to have high rumen concentrations of cellulolytic bacteria, ranging from 15% of the viable population in summer
to 35% in winter, compared to only 2.5% in Norwegian reindeer. Their rumen bacterial diversity was investigated through comparative
analyses of 16S rRNA gene sequences (∼1.5 kb in length) generated from clone libraries (n = 121) and bacterial isolates (n = 51). LIBSHUFF comparisons of the composition of the two 16S rRNA libraries from Norwegian reindeer showed a significant
effect of artificial feeding compared to natural pasture, but failed to yield significant differences between libraries from
Norwegian reindeer and Svalbard reindeer. The combined sequences from reindeer were not significantly different from those
reported in wild Thompson’s gazelle in Kenya but did differ from those reported in domestic cattle in Japan. A total of 90
distinct operational taxonomic units (OTUs) were identified by employing a criterion of 97% similarity, while the Chao1 index
estimated the reindeer bacterial rumen population richness at 698 OTUs. The majority of the clone library sequences (92.5%)
represented novel strains with <97% identity to any known sequence in the public database, most of them affiliated with the
bacterial phylum Firmicutes (low G+C Gram-positives) related to the order Clostridiales (76.7%), while Gram-negative bacteria in the Bacteriodales (Prevotella–Bacteroides group) contributed to 22.5%. Also, six of the isolates were putatively novel strains, possibly representing new species in
the Clostridium subphylum (cluster XIVa), Actinomyces and Butyrivibrio. 相似文献
974.
Rosa Gómez M. Isabel Arce J. Javier Sánchez M. del Mar Sánchez-Montoya 《Hydrobiologia》2012,679(1):43-59
Mediterranean climates predispose aquatic systems to both flood and drought periods, therefore, stream sediments may be exposed
to desiccation periods. Changes in oxygen concentrations and sediment water content influence the biotic processes implicated
in nitrogen dynamics. The objectives of this study were to identify (1) the changes of inorganic nitrogen in stream sediments
during the transition from wet to dry conditions, and (2) the underlying processes in N dynamics and its regulation. Extractable
sediment NO3
−-N and NH4
+-N, organic matter and extractable organic carbon content were assessed during natural desiccation in microcosms with sediments
from an intermittent Mediterranean stream. In agreement with our initial hypothesis, our results showed how the NO3
−-N content of the sediment was enhanced during the first 10 days of sediment drying, whereas NH4
+-N was lost by 14 days post-drying. During the first 10 days, sediment desiccation seemed to stimulate the net N-mineralization
and net nitrification from sediments. Afterwards, the extractable NO3
−-N concentration sharply dropped, which may be attributed to lower ammonium-oxidation rates as ammonium and organic matter
are depleted, and to an increase in NO3
−-N consumption by microbial populations. Denitrification was inhibited, with a significant decrease as % water-filled pore
space lowered. We hypothesize that the sediment inorganic N content enhanced during sediment desiccation could be released
as part of the N pulse observed after sediment rewetting. However, the stream N availability after rewetting dried sediments
would differ depending on desiccation period duration. 相似文献
975.
Eduardo Ribeiro Cunha Thaisa Sala Michelan Katya E. Kovalenko Sidinei Magela Thomaz 《Hydrobiologia》2012,685(1):19-26
Habitat complexity has long been known to influence animal community structure by increasing the number of available habitats.
Fifty years have passed since MacArthur brothers published the seminal paper “On bird species diversity”, which revolutionized
studies of habitat structure. This paper first evidenced and quantified the relationship between species diversity (birds)
and habitat structural complexity (the number of stratified layers of landscape vegetation). In this article, we aim to pay
homage to R. H. MacArthur’s contribution and to briefly analyze the citation history and influence of “On bird species diversity”,
focusing primarily on aquatic studies. We searched for all papers that cited “On bird species diversity” on Thomson Reuters
(ISI—Web of Knowledge) and analyzed them for temporal citation trends. In addition, considering only aquatic papers, we explored
whether and how habitat complexity was measured, as well as the ecological organization level, attributes of organisms, taxonomic
groups and study design (observational or experimental). “On bird species diversity” citations increased over time, but this
paper was less cited by limnologists compared to terrestrial and marine scientists. The majority of investigations in aquatic
ecosystems quantified habitat complexity, but few used mathematical modeling. The high number of citations, which continues
to increase, shows the great influence of “On bird species diversity” on ecological studies and typifies it as a classic in
the ecological literature. However, the low citation frequency found in papers devoted to freshwater ecosystems indicates
that limnologists in general neglect this original contribution in studies of habitat complexity. 相似文献
976.
This study describes the development of a micropropagation protocol for Pinguicula vulgaris using cultures initiated from in vitro produced seedlings. P. vulgaris is a carnivorous plant with a northern, disjunctly circumpolar distribution and specific habitat requirements, and is hence becoming increasingly rare. Shoot proliferation was significantly influenced by Murashige and Skoog (MS) macronutrient concentration, showing higher proliferation rates in 1/4MS, but was not affected by the addition of 0.1 mg/L 6-benzyladenine (BA) or zeatin (Zea). The best medium for propagating P. vulgaris was plant growth regulator (PGR) free ¼MS. An average of 7.62 new shoots per initial explant could be obtained after 8 weeks of culture, of which over 79% produced roots during proliferation. Moreover, rooting percentages of 100% were obtained for the initial explants in all the tested media, including media without PGRs. The plantlets were successfully acclimatized to ex vitro conditions, exhibiting normal development. 相似文献
977.
Imanishi S Kobayashi J Sekine T 《In vitro cellular & developmental biology. Animal》2012,48(3):137-142
We established the first continuous cell line that uses a serum-free culture from the embryo of Bombyx mori (Lepidoptera: Bombycidae), designated as NIAS-Bm-Ke17. This cell line was serially subcultured in the SH-Ke-117 medium. The
cells adhere weakly to the culture flask, and most cells have an oval shape. The cell line was subcultured 154 times, and
the population doubling time is 83.67 ± 5.22 h. Random amplification of polymorphic DNA-polymerase chain reaction with a tenmar
single primer for discrimination of insect cell lines recognized the NIAS-Bm-Ke1 cell line as B. mori. This cell line does not support the growth of the B. mori nuclear polyhedrosis virus (BmNPV) in the absence of the heat-inactivated hemolymph of B. mori. However, the heat-inactivated hemolymph in 1% volume of the medium supported a high level of susceptibility to BmNPV. In
addition, the cooling treatment of the cells at 2.5°C also enhanced the susceptibility. We report a new serum-free culture
system of the B. mori cell line for the baculovirus expression vector system. 相似文献
978.
979.
The kidney is an extremely complex organ with broad ranging functions in the body, including but not restricted to waste excretion,
ion and water balance, maintenance of blood pressure, glucose homeostasis, generation of erythropoietin and activation of
vitamin D. With diabetes, many of these integral processes are interrupted via a combination of haemodynamic and metabolic
changes including increases in the accumulation of proteins modified by advanced glycation, known as advanced glycation end
products (AGEs). Indeed, hyperglycaemia and the redox imbalances seen with diabetes are each independent accelerants for the
production of AGEs, which synergistically combine in this disorder. In addition, as kidney function declines, characterised
by a loss of glomerular filtration, the excretion of AGEs is decreased, possibly exacerbating renal injury by further elevating
the body’s tissue and circulating AGE pool. Therefore, it has become apparent that decreasing the accumulation of AGEs or
interrupting their downstream effects on the kidney, are desirable therapeutic targets for the treatment of diabetic renal
disease. 相似文献
980.