全文获取类型
收费全文 | 216690篇 |
免费 | 9481篇 |
国内免费 | 902篇 |
专业分类
227073篇 |
出版年
2023年 | 689篇 |
2022年 | 735篇 |
2021年 | 1579篇 |
2020年 | 1336篇 |
2019年 | 1423篇 |
2018年 | 14371篇 |
2017年 | 12902篇 |
2016年 | 10947篇 |
2015年 | 6383篇 |
2014年 | 6310篇 |
2013年 | 8243篇 |
2012年 | 13601篇 |
2011年 | 20953篇 |
2010年 | 16909篇 |
2009年 | 12140篇 |
2008年 | 16359篇 |
2007年 | 17723篇 |
2006年 | 6856篇 |
2005年 | 6682篇 |
2004年 | 6777篇 |
2003年 | 6342篇 |
2002年 | 5724篇 |
2001年 | 2939篇 |
2000年 | 2765篇 |
1999年 | 2302篇 |
1998年 | 1093篇 |
1997年 | 843篇 |
1996年 | 767篇 |
1995年 | 750篇 |
1994年 | 707篇 |
1993年 | 606篇 |
1992年 | 1488篇 |
1991年 | 1396篇 |
1990年 | 1220篇 |
1989年 | 1134篇 |
1988年 | 1067篇 |
1987年 | 909篇 |
1986年 | 859篇 |
1985年 | 922篇 |
1984年 | 782篇 |
1983年 | 657篇 |
1982年 | 530篇 |
1981年 | 493篇 |
1979年 | 654篇 |
1978年 | 523篇 |
1975年 | 488篇 |
1974年 | 504篇 |
1973年 | 515篇 |
1972年 | 630篇 |
1971年 | 671篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
F Krizsa Z Borbényi E Arokszállásy I Cserháti 《Folia haematologica (Leipzig, Germany : 1928)》1980,107(4):683-687
The thrombopoietic serum activity was examined in rats during thrombocytopenia produced by bleeding or after treatment with antithrombocyte serum (ATS). 6 hours after both treatments the thrombopoietic activity of the serum, i.e. its content of thrombopoietin, is increased. After the ATS treatment of nephrectomized animals a similar increase of thrombopoietic activity as in normal animals could be achieved. In contrast to that, no similar increase of thrombopoietic activity was observed in nephrectomized animals after blood loss. According to the results of the authors the increase of thrombopoietic activity produced by different stimuli can be attributed to different mechanisms. 相似文献
72.
Jianhua Zhang Mei Liu Hongjian Jin Liandong Deng Jinfeng Xing Anjie Dong 《AAPS PharmSciTech》2010,11(2):894-903
Lactate esters are widely used as food additives, perfume materials, medicine additives, and personal care products. The objective
of this work was to investigate the effect of a series of lactate esters as penetration enhancers on the in vitro skin permeation of four drugs with different physicochemical properties, including ibuprofen, salicylic acid, dexamethasone
and 5-fluorouracil. The saturated donor solutions of the evaluated drugs in propylene glycol were used in order to keep a
constant driving force with maximum thermodynamic activity. The permeability coefficient (K
p), skin concentration of drugs (SC), and lag time (T), as well as the enhancement ratios for K
p and SC were recorded. All results indicated that lactate esters can exert a significant influence on the transdermal delivery
of the model drugs and there is a structure-activity relationship between the tested lactate esters and their enhancement
effects. The results also suggested that the lactate esters with the chain length of fatty alcohol moieties of 10–12 are more
effective enhancers. Furthermore, the enhancement effect of lactate esters increases with a decrease of the drug lipophilicity,
which suggests that they may be more efficient at enhancing the penetration of hydrophilic drugs than lipophilic drugs. The
influence of the concentration of lactate esters was evaluated and the optimal concentration is in the range of 5∼10 wt.%.
In sum, lactate esters as a penetration enhancer for some drugs are of interest for transdermal administration when the safety
of penetration enhancers is a prime consideration. 相似文献
73.
74.
Hugues Bersini 《Origins of life and evolution of the biosphere》2010,40(2):121-130
There is a long tradition of software simulations in theoretical biology to complement pure analytical mathematics which are
often limited to reproduce and understand the self-organization phenomena resulting from the non-linear and spatially grounded
interactions of the huge number of diverse biological objects. Since John Von Neumann and Alan Turing pioneering works on
self-replication and morphogenesis, proponents of artificial life have chosen to resolutely neglecting a lot of materialistic
and quantitative information deemed not indispensable and have focused on the rule-based mechanisms making life possible,
supposedly neutral with respect to their underlying material embodiment. Minimal life begins at the intersection of a series
of processes which need to be isolated, differentiated and duplicated as such in computers. Only software developments and
running make possible to understand the way these processes are intimately interconnected in order for life to appear at the
crossroad. In this paper, I will attempt to set out the history of life as the disciples of artificial life understand it,
by placing these different lessons on a temporal and causal axis, showing which one is indispensable to the appearance of
the next and how does it connect to the next. I will discuss the task of artificial life as setting up experimental software
platforms where these different lessons, whether taken in isolation or together, are tested, simulated, and, more systematically,
analyzed. I will sketch some of these existing software platforms: chemical reaction networks, Varela’s autopoietic cellular
automata, Ganti’s chemoton model, whose running delivers interesting take home messages to open-minded biologists. 相似文献
75.
Biogeographical analyses are applied to skipper (Hesperioidea) presence/absence data from the Western Mediterranean mainland
and the three largest islands (Sardinia, Corsica and Sicily) in order to identify potential conservation issues. The analyses
performed on species, both collectively and individually, indicate that regional species richness and occurrence in the Mediterranean
zone are largely predicted by latitude and area but that islands have impoverished faunas. Several species, predicted to be
present on these islands from logistic regression of their continental distributions, are actually absent. The number of species
predicted to be present from logistic regression analyses for each island, closely matched the number of species predicted
to occur in regional-focused multiple regression analysis. This suggests that missing species have been identified. When compared
with species that occur in Sicily and Corsica, the missing species are shown to differ for ecological traits, mainly those
linked to altitudinal tolerance. No ecological distinctions were disclosed for Sardinian skippers suggesting a mainly stochastic
colonisation. These results, and those from an analogous study carried out on Papilionoidea, point to Hesperioidea having
(i) overall more impoverished faunas on islands and (ii) being subject to stochastic or historical colonisation events more
than Papilionoidea. Species not predicted to occur on islands based on their mainland distributions and ecological traits,
are foci for conservation attention. However, as many species becoming extinct on the islands may be irreplaceable, all species,
in particular the Sardinian ones, deserve to be conserved. 相似文献
76.
Hiroyuki Kozu Isao Kobayashi Mitsutoshi Nakajima Kunihiko Uemura Seigo Sato Sosaku Ichikawa 《Food biophysics》2010,5(4):330-336
This paper uses computational fluid dynamics to simulate and analyze intragastric fluid motions induced by human peristalsis.
We created a two-dimensional computational domain of the distal stomach where peristalsis occurs. The motion of the gastric
walls induced by an antral contraction wave (ACW) on the wall of the computational domain was well simulated using a function
defined in this study. Retropulsive flow caused by ACW was observed near the occluded region, reaching its highest velocity
of approximately 12 mm/s in the narrowest region. The viscosity of the model gastric contents applied in this study hardly
affected the highest velocity, but greatly affected the velocity profile in the computational domain. The shear rate due to
gastric fluid motion was calculated using the numerical output data. The shear rate reached relatively high values of approximately
20 s−1 in the most occluded region. The shear rate profile was almost independent of the fluid viscosity. We also simulated mass
transfer of a gastric digestive enzyme (pepsin) in model gastric content when peristalsis occurs on the gastric walls. The
visualized simulation results suggest that gastric peristalsis is capable of efficiently mixing pepsin secreted from the gastric
walls with an intragastric fluid. 相似文献
77.
78.
F García J Sánchez J Planas 《Comparative biochemistry and physiology. A, Comparative physiology》1987,87(4):947-950
1. Male quails submitted 20 and 120 days to a low iron diet (7 ppm) were compared to female laying quails, exposed for 30 days to the same low iron regime, in order to compare the response of the iron metabolic control under a single (erythropoiesis) or a doubled (erythropoiesis and egg formation) iron demand. 2. Iron deposit in storage organs, the classical hematology and the intestinal iron absorption were analyzed in these animals. 3. In males, after 120 days, the iron deposits were reduced 50 and 75%, but hematological values (hematocrit and hemoglobin concentration) were normal, although in laying quails, after 30 days, an anemic condition was evident in both blood parameters and iron deposits, provoking an iron deficient erythropoiesis. 4. The enhancement of the intestinal iron uptake, confirms the anemic character of these birds. 相似文献
79.
A Rhalem K Bekhti C Bourdieu G Luffau P Péry 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1989,309(1):19-23
Proteins are released from the surface of sporozoites of Eimeria falciformis during their in vitro incubation in a detergent solution. Some of these proteins reacted with antibodies from infected mice and specifically stimulated the proliferation of mesenteric lymph node cells of these mice. Oral immunization of mice with liposome encapsulated sporozoite surface antigens protected mice against a challenge infection. Two proteins (M.W. 27 and 180 K) induced an antibody synthesis in these vaccinated mice. 相似文献
80.
J R David P Gibert G Pétavy B Moreteau 《Proceedings. Biological sciences / The Royal Society》2002,269(1487):127-135
We investigated body-size inheritance in interspecific sterile hybrids by crossing a Drosophila simulans strain with 13 strains of Drosophila melanogaster, which were of various origins and chosen for their broad range of genetic variation. A highly significant parent-offspring correlation was observed, showing that the D. melanogaster genes for size are still expressed in a hybrid background. Superimposed on to this additive inheritance, the size of hybrids was always less than the mid-parent value. This phenomenon, which at first sight might be described as dominance or overdominance, is more precisely interpreted as a consequence of a hybrid breakdown, that is, a dysfunction of the parental genes for size when put to work together. This interpretation is enforced by the fact that phenotypic variability was much more prevalent in hybrids than in parents. We also analysed body pigmentation inheritance in the same crosses and got a very different picture. There was no increase in the phenotypic variance of F(1) hybrids and only a low parent-offspring correlation. Apparent overdominance could be observed but in opposite directions, with no evidence of hybrid breakdown. Our data point to the possibility of analysing a diversity of quantitative traits in interspecific hybrids, and indicate that breakdown might be restricted to some traits only. 相似文献