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971.
Indian ricegrass ( Achnatherum hymenoides [Roem. & Schult.] Barkworth) is a rangeland species native to western North America with populations that may exhibit distinct seed-size morphs borne on separate plants. These morphs are often associated with very different levels of seed dormancy. We compared RAPD profiles of the relatively infrequent and highly dormant jumbo seed morph to its more germinable small or large (non-jumbo) companion seed morphs collected from 9 sites where they were sympatric. Jumbo seed accessions from 9 additional sites that did not exhibit seed polymorphism were included to better sample this seed morph across the species' range. Sympatric seed morphs were consistently distinguishable by their RAPD profiles, and sympatric seed morphs were no more likely to cluster together than nonsympatric seed morphs. The ability of sympatric seed morphs to maintain their genetic identity is compatible with the hypothesis of a predominately autogamous breeding system. Furthermore, these data support the hypothesis that local polymorphic populations result from overlapping waves of migration with distinct geographical origins. The jumbo seed morphs exhibited moderate correlation between genetic distance and geographic distance, but the non-jumbo seed morphs exhibited no such correlation. Jumbo seed morphs that were collected at or east of the Continental Divide in New Mexico and Colorado are more genetically homogeneous than those west of the Continental Divide, and non-jumbo seed morphs from the east are more genetically variable than jumbo seed morphs from the same locations. This suggests that gene flow eastward across the Rocky Mountains has been more frequent for the non-jumbo seed morphs than for the jumbo seed morphs. 相似文献
972.
Preparatory changes in neural activity before the execution of a movement have been documented in tasks that involve an instructed delay period (an interval between a transient instruction cue and a subsequently triggered movement). Such preparatory activity occurs in many motor centres in the brain, including the primary motor cortex, premotor cortex, supplementary motor area and basal ganglia. Activity during the instructed delay period reflects movement planning, as it correlates with parameters of the cue and the subsequent movement (such as direction and extent), although it occurs well before muscle activity. How such delay-period activity shapes the ensuing motor action remains unknown. Here we show that spinal interneurons also exhibit early pre-movement delay activity that often differs from their responses during the subsequent muscle activity. This delay activity resembles the set-related activity found in various supraspinal areas, indicating that movement preparation may occur simultaneously over widely distributed regions, including spinal levels. Our results also suggest that two processes occur in the spinal circuitry during this delay period: the motor network is primed with rate changes in the same direction as subsequent movement-related activity; and a superimposed global inhibition suppresses the expression of this activity in muscles. 相似文献
973.
我们利用月球侦察轨道器(LRO)的窄角相机(NAC)数据,使用一种新的光学遥感方法—相比率影像法,来评估月表亚分辨率尺度的粗糙度.我们用该方法对月面谷Vallis Schrteri地区的三维相比率影像进行分析后发现,在月面谷侧面上风化物的复杂运动模式与撞击坑并无关联,而是由风化物和岩屑形成的,而非冲击熔融. 相似文献
974.
The substrate- and inhibitor-related characteristics of monoamine oxidase (MAO) were studied on chick brain mitochondria. It was found that neither 5-hydroxytryptamine nor beta-phenylethylamine is the specific substrate for type A and type B MAO in chick brain. 相似文献
975.
976.
Peripheral blood samples from 52 women, including 16 with herpes genitalis and 36 healthy persons, were studied to enumerate subpopulations of lymphocytes. It was found that the mean percentage of 'active' T lymphocytes was significantly less in the patients with herpes genitalis than in the controls. 相似文献
977.
Under in vitro experimental conditions in which insulin increases adipose tissue lipoprotein lipase, cyclic GMP or dibutyryl cyclic GMP has no effect on this enzyme in rat adipose tissue fragments, or on either the intra- or extracellular forms of this enzyme in isolated fat cells. These results do not support the involvement of cyclic GMP in the insulin-stimulation of lipoprotein lipase in adipose tissue. 相似文献
978.
In the present paper we report examination of stereotypic hallmarks of apoptosis in heat-treated tobacco cells. Hyperthermia
(44 °C, 4 h) caused apoptosis in 53.6% of cells when assayed 24 h after heat treatment. The induction of apoptosis by heat
treatment was confirmed by flow cytometric assay. Cytological observations revealed condensation of the cytoplasm and nucleus,
as well as nuclear collapse. DNA ladders were observed in DNA extracted from heat-treated cells, whereas DNA from control
cells remained undegraded. The terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay revealed
that 51.8% of the heat-treated cells (44 °C, 4 h) show positive reaction after a 24-h recovery. When cells were cultured in
a medium supplemented with 0.4–5.0 mM ZnSO4, internucleosomal DNA fragmentation induced by heat shock was completely negated. Strikingly, when cells were cultured in
Ca2+ and/or Mg2+ free medium for 44 h followed by heat treatment, DNA laddering was not observed. The results suggest hyperthermia-induced
apoptosis and a correlation between the regula tion of endonucleases and heat shock signal in apoptotic tobacco cells.
Received 17 September 1998; received after revision 4 January 1999; accepted 4 January 1999 相似文献
979.
It is easy to apply lines in design drawings to create different styles, however, there is no guarantee that all the style lines drawn are able to be manufactured. In this paper, we focus on one undeliverable style to enhance our understanding of the relationship between the design sketch and the pattern design process. In order to evidence that such style is unworkable, a systematic display of pattern development, and to be reinforced by mathematical evaluation, will be introduced and addressed. When one can easily detect design fault, waste of product development time can be minimized. 相似文献
980.
E A Lindsay A Botta V Jurecic S Carattini-Rivera Y C Cheah H M Rosenblatt A Bradley A Baldini 《Nature》1999,401(6751):379-383
The heterozygous chromosome deletion within the band 22q11 (del22q11) is an important cause of congenital cardiovascular defects. It is the genetic basis of DiGeorge syndrome and causes the most common deletion syndrome in humans. Because the deleted region is largely conserved in the mouse, we were able to engineer a chromosome deletion (Df1) spanning a segment of the murine region homologous to the human deleted region. Here we describe heterozygously deleted (Df1/+) mice with cardiovascular abnormalities of the same type as those associated with del22q11; we have traced the embryological origin of these abnormalities to defective development of the fourth pharyngeal arch arteries. Genetic complementation of the deletion using a chromosome duplicated for the Df1 DNA segment corrects the heart defects, indicating that they are caused by reduced dosage of genes located within Df1. The Df1/+ mouse model reveals the pathogenic basis of the most clinically severe aspect of DiGeorge syndrome and uncovers a new mechanism leading to aortic arch abnormalities. These mutants represent a mouse model of a human deletion syndrome generated by chromosome engineering. 相似文献