全文获取类型
收费全文 | 14006篇 |
免费 | 1205篇 |
国内免费 | 1篇 |
专业分类
15212篇 |
出版年
2024年 | 20篇 |
2023年 | 146篇 |
2022年 | 93篇 |
2021年 | 217篇 |
2020年 | 208篇 |
2019年 | 212篇 |
2018年 | 572篇 |
2017年 | 472篇 |
2016年 | 502篇 |
2015年 | 405篇 |
2014年 | 428篇 |
2013年 | 795篇 |
2012年 | 1129篇 |
2011年 | 1294篇 |
2010年 | 668篇 |
2009年 | 437篇 |
2008年 | 959篇 |
2007年 | 865篇 |
2006年 | 853篇 |
2005年 | 645篇 |
2004年 | 679篇 |
2003年 | 628篇 |
2002年 | 568篇 |
2001年 | 415篇 |
2000年 | 526篇 |
1999年 | 260篇 |
1998年 | 137篇 |
1997年 | 98篇 |
1996年 | 93篇 |
1995年 | 77篇 |
1994年 | 77篇 |
1993年 | 74篇 |
1992年 | 70篇 |
1991年 | 66篇 |
1990年 | 42篇 |
1989年 | 32篇 |
1988年 | 31篇 |
1987年 | 30篇 |
1986年 | 16篇 |
1985年 | 40篇 |
1984年 | 32篇 |
1983年 | 29篇 |
1982年 | 37篇 |
1981年 | 25篇 |
1980年 | 22篇 |
1979年 | 23篇 |
1978年 | 22篇 |
1977年 | 20篇 |
1974年 | 19篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Carricaburu P Muñoz-Cuevas A 《Comptes rendus des séances de la Société de biologie et de ses filiales》1998,192(6):1163-1173
Injections of modafinil, a drug able to induce in vertebrates an awakening effect via an effective central alpha 1-adrenergic tone, induce modifications of the amplitude and latency of electroretinograms (ERGs) in the spider Lycosa tarentula, during dark adaptation. Results of experiments are different from one eye type to another as circadian activity rhythms of the retinae also differ. Modafinil induces a decrease of diurnal amplitudes and has no effect on nocturnal amplitudes of ERGs of anterior-lateral eyes; in the case of posterior-median eyes, the amplitudes are increased in daytime as well as at night. Prazosin, antagonist of alpha 1-adrenergic receptors, injected after modafinil, induces a decrease of the amplitudes of ERGs in the same eyes. These results are discussed in relation to the visual activity of this species, both diurnal and nocturnal. The concepts of waking state versus sleep are not precisely characterized in arachnids, so that the effects of modafinil on L. tarentula may not be considered like those described in vertebrates. 相似文献
942.
A cereal cyst nematode (Heterodera avenae Woll.) resistance gene transferred from Aegilops triuncialis to hexaploid wheat 总被引:1,自引:0,他引:1
M. D. Romero M. J. Montes E. Sin I. Lopez-Braña A. Duce J. A. Martín-Sanchez M. F. Andrés A. Delibes 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,96(8):1135-1140
The cereal cyst nematode (Heterodera avenae) is an important root parasite of common wheat. A high level of resistance was transferred to wheat from Aegilops triuncialis (TR lines) using the cross [(T. turgidum×Ae. triuncialis)×T. aestivum]. Low fertility (3–5 viable kernels per plant) was observed during the process but the surviving hybrid plants were highly
vigorous. To obtain stable resistant lines further crosses to T. aestivum were performed. The resistance in TR lines seems to be transferred from the C genome of Ae. triuncialis (genomes CCUU). Ae. triuncialis was highly resistant to the two Spanish populations of H. avenae tested, as well as to four French races and two Swedish populations. The histological analysis showed a hypersensitive reaction
in the roots of a resistant TR line inoculated with the Ha71 pathotype of H. avenae, whereas well-formed syncytia were observed in the roots of the susceptible control. Resistance to the H. avenae Ha71 pathotype seemed to be inherited as determined by a single dominant factor in the crosses between resistant TR lines
and susceptible cultivars.
Received: 11 November 1997 / Accepted: 9 December 1997 相似文献
943.
Thirty-two barley cultivars grown in Spain, 18 of the two-row type and 14 of the six-row type, were screened for plant regeneration
from cultured immature embryos. Although there was much variation in regeneration capacity among the cultivars, plants were
obtained from all cultivars except Almunia. No statistical differences were found in the percentage of regeneration between
two- and six-row types. The influence of the auxins 2,4-dichlorophenoxyacetic acid, dicamba, and picloram on the induction
and maintenance of embryogenesis and regeneration capacity after 3–4 months in culture, were evaluated for cultivars Cobra,
Hop and Reinette. Hop had the highest rates of maintenance of embryogenic capacity and plant regeneration. The medium containing
dicamba gave the best embryogenic callus induction, maintenance and regeneration. Five regeneration media, differing in growth
regulators and micronutrient composition, as well as partial desiccation of the calli before regeneration, were tested. The
regeneration medium containing 10 μm copper sulfate gave the best results. Regeneration frequencies after 3–4 months in culture of cultivar Hop were raised from
59.5 to 93.7% in this medium. Silver nitrate and partial desiccation of the calli also enhanced plant regeneration, but the
medium containing 10 μm of silver nitrate reduced root formation.
Received: 30 October 1997 / Revision received: 3 April 1998 / Accepted: 17 April 1998 相似文献
944.
Phylogenetic utility of the nuclear gene arginine decarboxylase: an example from Brassicaceae 总被引:10,自引:2,他引:8
Arginine decarboxylase (ADC) is an important enzyme in the production of
putrescine and polyamines in plants. It is encoded by a single or low-copy
nuclear gene that lacks introns in sequences studied to date. The rate of
Adc amino acid sequence evolution is similar to that of ndhF for the
angiosperm family studied. Highly conserved regions provide several target
sites for PCR priming and sequencing and aid in nucleotide and amino acid
sequence alignment across a range of taxonomic levels, while a variable
region provides an increased number of potentially informative characters
relative to ndhF for the taxa surveyed. The utility of the Adc gene in
plant molecular systematic studies is demonstrated by analysis of its
partial nucleotide sequences obtained from 13 representatives of
Brassicaceae and 3 outgroup taxa, 2 from the mustard oil clade (order
Capparales) and 1 from the related order Malvales. Two copies of the Adc
gene, Adc1 and Adc2, are found in all members of the Brassicaceae studied
to data except the basal genus Aethionema. The resulting Adc gene tree
provides robust phylogenetic data regarding relationships within the
complex mustard family, as well as independent support for proposed tribal
realignments based on other molecular data sets such as those from
chloroplast DNA.
相似文献
945.
John A. White Carson C. Chow Jason Rit Cristina Soto-Treviño Nancy Kopell 《Journal of computational neuroscience》1998,5(1):5-16
We study some mechanisms responsible for synchronous oscillations and loss of synchrony at physiologically relevant frequencies (10–200 Hz) in a network of heterogeneous inhibitory neurons. We focus on the factors that determine the level of synchrony and frequency of the network response, as well as the effects of mild heterogeneity on network dynamics. With mild heterogeneity, synchrony is never perfect and is relatively fragile. In addition, the effects of inhibition are more complex in mildly heterogeneous networks than in homogeneous ones. In the former, synchrony is broken in two distinct ways, depending on the ratio of the synaptic decay time to the period of repetitive action potentials (s/T), where T can be determined either from the network or from a single, self-inhibiting neuron. With s/T > 2, corresponding to large applied current, small synaptic strength or large synaptic decay time, the effects of inhibition are largely tonic and heterogeneous neurons spike relatively independently. With s/T < 1, synchrony breaks when faster cells begin to suppress their less excitable neighbors; cells that fire remain nearly synchronous. We show numerically that the behavior of mildly heterogeneous networks can be related to the behavior of single, self-inhibiting cells, which can be studied analytically. 相似文献
946.
Fanjul-Moles ML Bosques-Tistler T Prieto-Sagredo J Castañón-Cervantes O Fernández-Rivera-Río L 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》1998,119(1):263-269
The effects of light intensity and duration on metabolic and behavioral parameters of two species of crayfish, Procambarus clarkii and Procambarus digueti, were studied. Sixty animals of each species were submitted to high irradiance conditions of two different photoperiod lengths, one normal light/dark (LD) 12:12 and one extreme LD 20:4 for 2 weeks. Hemolymph, lactate and oxygen consumption were determined throughout the experimental period. Simultaneously in 18 additional animals of each species, motor activity was individually recorded under the same control and experimental conditions. Both species showed a decrease in oxygen uptake and an increase in hemolymph lactate concentration. The statistical significance of this finding was higher for LD 20:4. This extreme condition evoked a significant decrease of motor activity in P. clarkii and a high mortality rate in P. digueti. P. digueti did not survive after the experiment, whereas P. clarkii survived and adapted to the laboratory conditions. Changes in metabolic and behavioral parameters could indicate different adaptation abilities in these species. 相似文献
947.
Comparative study of microbiological and histopathological techniques used for the detection of Helicobacter pylori 总被引:3,自引:0,他引:3
Muñoz E Corcuera MT Roldán M Gómez F Picazo A Baquero M Alonso MJ 《European journal of histochemistry : EJH》1998,42(4):297-302
This study evaluates the sensitivity, specificity and predictive values of several techniques commonly used for the detection of Helicobacter pylori in an analysis of 105 biopsy specimens (gastric and duodenal). For comparative purposes, the techniques investigated were divided into 2 groups: histopathological and microbiological. The former included hematoxylin-eosin and Giemsa stains, a Gram stain modified for use in tissue, and immunohistochemical techniques. Microbiological analysis was performed using culture, the urease test and the conventional Gram stain. The immunohistochemical techniques proved to be the most sensitive (93%). The modified Gram stain was sufficiently sensitive (92%) and specific (97%) for the detection of the bacterium. When combined with a microbiological technique such as the urease test, this stain showed increased sensitivity (96%) but its specificity was reduced to 94%. This combination of tests is recommended for the detection of H. pylori in biopsy specimens since it is easily performed at low cost and gives excellent results. For economical reasons, it is suggested that the use of immunohistochemical techniques should be restricted to specific cases. 相似文献
948.
Ceballos Salobreña A Gaitán Cepeda LA Ruesga MT Ceballos García L Quindós G 《Revista iberoamericana de micología》1998,15(3):141-145
The aim of this study has been to determine the prevalence of oral candidiasis and oral Candida carriers in an AIDS population under highly active antiretroviral therapy. Eighty-six AIDS patients treated with an antiretroviral combination (indinavir o ritonavir o saquinavir + zidovudine [AZT] + lamivudine [3TC]). Patients were grouped attending the predisposing factors for HIV infection in: intravenous drug users (IDU), heterosexuals, homosexuals, patients using hematological products or having unknown factors. Oral cavity was examined and an oral specimen was inoculated in a chromogenic culture medium (Albicans ID, bioMérieux, France). The prevalence of oral Candida lesions was 30.2% and Candida was isolated from 54.7% of patients. The predominant species was C. albicans serotype A in all the groups with the exception of homosexual patients, were C. albicans serotype B was the predominant. The IDU group showed the higher prevalence of Candida lesions and oral yeasts colonization, followed by the group of heterosexuals and homosexuals. An association was found between the presence of lesions and/or Candida spp. and the clinical stage or the viral concentration. The species Candida dubliniensis was isolated in the oral samples of two patients with candidosis and in two individuals without oral candidosis. The finding of this species in Spanish patients can be added to the data obtained in epidemiological studies in other countries. 相似文献
949.
Trichophyton simii in a "Caí" monkey (Cebus apella) colony in the province of Corrientes, Argentina.
Boehringer SI Cicuta ME Santa Cruz A Gómez L Patiño EM Borda JT 《Revista iberoamericana de micología》1998,15(4):300-301
The objective is to describe an outbreak of Trichophyton simii in a Cebus apella monkey colony in Argentine. During summer, alopecic zones appeared on dorsal regions from head to base of the tail of the animals. The hair and skin of nine animals were streaked onto Sabouraud dextrose with cloramphenicol and incubated at 25 degrees C. By the 10th day, white, filamentous colonies, which turned pale pink, developed from simples of four animals. Microscopical examinations were carried out and, because of colony and macroconidia morphology, were classified as Trichopyton simii. Although infection with T. simii is considered a zoonosis, we did not find human cases. 相似文献
950.