全文获取类型
收费全文 | 5977篇 |
免费 | 846篇 |
国内免费 | 3篇 |
专业分类
6826篇 |
出版年
2021年 | 78篇 |
2019年 | 55篇 |
2016年 | 84篇 |
2015年 | 128篇 |
2014年 | 165篇 |
2013年 | 217篇 |
2012年 | 274篇 |
2011年 | 271篇 |
2010年 | 153篇 |
2009年 | 155篇 |
2008年 | 226篇 |
2007年 | 203篇 |
2006年 | 216篇 |
2005年 | 197篇 |
2004年 | 215篇 |
2003年 | 163篇 |
2002年 | 195篇 |
2001年 | 176篇 |
2000年 | 190篇 |
1999年 | 174篇 |
1998年 | 104篇 |
1997年 | 57篇 |
1996年 | 73篇 |
1995年 | 87篇 |
1994年 | 77篇 |
1993年 | 75篇 |
1992年 | 144篇 |
1991年 | 148篇 |
1990年 | 126篇 |
1989年 | 142篇 |
1988年 | 135篇 |
1987年 | 121篇 |
1986年 | 107篇 |
1985年 | 95篇 |
1984年 | 88篇 |
1983年 | 89篇 |
1982年 | 60篇 |
1981年 | 69篇 |
1980年 | 56篇 |
1979年 | 99篇 |
1978年 | 69篇 |
1977年 | 78篇 |
1976年 | 68篇 |
1975年 | 77篇 |
1974年 | 95篇 |
1973年 | 74篇 |
1972年 | 78篇 |
1971年 | 67篇 |
1970年 | 66篇 |
1968年 | 54篇 |
排序方式: 共有6826条查询结果,搜索用时 0 毫秒
151.
Stevenson PC Green PW Stevenson PC Simmonds MS Sharma HC 《Bulletin of entomological research》2002,92(1):45-51
Experiments were conducted to observe the feeding and food selection-behaviour of different instars of the pod-borer Helicoverpa armigera (Hübner) in response to choices between the cultivated and a wild species of Cajanus. First and second instars fed upon a cultivated variety of Cajanus cajan in preference to a wild species, C. scarabaeoides and on flowers of C. cajan, rather than pods or leaves of C. cajan. First and second instars preferred pods of C. scarabaeoides with trichomes removed to pods with trichomes present. All instars fed upon pods of C. cajan rather than those of C. scarabaeoides. Solvent extraction of the pod surfaces affected the feeding of larvae, in some instances. They preferred the unextracted pods of C. cajan; the extracted pod of C. scarabaeoides (first and second instars) or the unextracted pod of C. scarabaeoides (fourth and fifth instars). Glass-fibre disc bioassays showed that the methanol, hexane and water extracts from the pod-surface of C. cajan stimulated the feeding of fifth instars. The experiments have shown that characteristics of C. cajan, such as either the compounds present or the type and distribution of trichomes on the plant surfaces, can determine the susceptibility of C. cajan to pod-borer larvae. 相似文献
152.
Lanningham-Foster L Green CL Langkamp-Henken B Davis BA Nguyen KT Bender BS Cousins RJ 《American journal of physiology. Endocrinology and metabolism》2002,282(6):E1197-E1203
Cysteine-rich intestinal protein (CRIP), which contains a double zinc finger motif, is a member of the Group 2 LIM protein family. Our results showed that the developmental regulation of CRIP in neonates was not influenced by conventional vs. specific pathogen-free housing conditions. Thymic and splenic CRIP expression was not developmentally regulated. A line of transgenic (Tg) mice that overexpress the rat CRIP gene was created. When challenged with lipopolysaccharide, the Tg mice lost more weight, exhibited increased mortality, experienced greater diarrhea incidence, and had less serum interferon-gamma (IFN-gamma) and more interleukin (IL)-6 and IL-10. Similarly, splenocytes from the Tg mice produced less IFN-gamma and IL-2 and more IL-10 and IL-6 upon mitogen stimulation. Delayed-type hypersensitivity response was less in the Tg mice. Influenza virus infection produced greater weight loss in the Tg mice, which also showed delayed viral clearance. The observed responses to overexpression of the CRIP gene are consistent with a role for this LIM protein in a cellular pathway that produces an imbalance in cytokine pattern favoring Th2 cytokines. 相似文献
153.
T. Wakabayashi E. F. Korman D. E. Green 《Journal of bioenergetics and biomembranes》1971,2(5-6):233-247
A set of six biological membranes has been examined electron microscopically in positively-stained sections at both low and high resolution. At low resolution, all six membranes exhibit a railroad track pattern, while at high resolution all six membranes exhibit a pattern of a double-tier of globular particles. The correspondence between the railroad track pattern and the double-tiered pattern is considered. The relationship of the double-tiered pattern to the bimodal properties of the constituent protein and phospholipid molecules is discussed. 相似文献
154.
Fermentative production of butanol--the industrial perspective 总被引:1,自引:0,他引:1
Green EM 《Current opinion in biotechnology》2011,22(3):337-343
A sustainable bacterial fermentation route to produce biobutanol is poised for re-commercialization. Today, biobutanol can compete with synthetic butanol in the chemical market. Biobutanol is also a superior biofuel and, in longer term, can make an important contribution towards the demand for next generation biofuels. There is scope to improve the conventional fermentation process with solventogenic clostridia and drive down the production cost of 1-butanol by deploying recent advances in biotechnology and engineering. This review describes re-commercialization efforts and highlights developments in feedstock utilization, microbial strain development and fermentation process development, all of which significantly impact production costs. 相似文献
155.
Komlavi Anani Afanou Anne Straumfors Asbj?rn Skogstad Ajay P. Nayak Ida Skaar Linda Hjeljord Arne Tronsmo Wijnand Eduard Brett James Green 《Applied and environmental microbiology》2015,81(17):5794-5803
Submicronic fungal fragments have been observed in in vitro aerosolization experiments. The occurrence of these particles has therefore been suggested to contribute to respiratory health problems observed in mold-contaminated indoor environments. However, the role of submicronic fragments in exacerbating adverse health effects has remained unclear due to limitations associated with detection methods. In the present study, we report the development of an indirect immunodetection assay that utilizes chicken polyclonal antibodies developed against spores from Aspergillus versicolor and high-resolution field emission scanning electron microscopy (FESEM). Immunolabeling was performed with A. versicolor fragments immobilized and fixed onto poly-l-lysine-coated polycarbonate filters. Ninety percent of submicronic fragments and 1- to 2-μm fragments, compared to 100% of >2-μm fragments generated from pure freeze-dried mycelial fragments of A. versicolor, were positively labeled. In proof-of-concept experiments, air samples collected from moldy indoor environments were evaluated using the immunolabeling technique. Our results indicated that 13% of the total collected particles were derived from fungi. This fraction comprises 79% of the fragments that were detected by immunolabeling and 21% of the spore particles that were morphologically identified. The methods reported in this study enable the enumeration of fungal particles, including submicronic fragments, in a complex heterogeneous environmental sample. 相似文献
156.
Basnayake SD Hyam JA Pereira EA Schweder PM Brittain JS Aziz TZ Green AL Paterson DJ 《Journal of applied physiology (Bethesda, Md. : 1985)》2011,110(4):881-891
Groups III and IV afferents carry sensory information regarding the muscle exercise pressor reflex, although the central integrating circuits of the reflex in humans are still poorly defined. Emerging evidence reports that the periaqueductal gray (PAG) could be a major site for integrating the "central command" component that initiates the cardiovascular response to exercise, since this area is activated during exercise and direct stimulation of the dorsal PAG causes an increase in arterial blood pressure (ABP) in humans. Here we recorded local field potentials (LFPs) from various "deep" brain nuclei during exercise tasks designed to elicit the muscle pressor reflex. The patients studied had undergone neurosurgery for the treatment of movement or pain disorders, thus had electrodes implanted stereotactically either in the PAG, subthalamic nucleus, globus pallidus interna, thalamus, hypothalamus, or anterior cingulate cortex. Fast Fourier transform analysis was applied to the neurograms to identify the power of fundamental spectral frequencies. Our PAG patients showed significant increases in LFP power at frequencies from 4 to 8 Hz (P < 0.01), 8 to 12 Hz (P < 0.001), and 12 to 25 Hz (P < 0.001). These periods were associated with maintained elevated ABP during muscle occlusion following exercise. Further increases in exercise intensity resulted in corresponding increases in PAG activity and ABP. No significant changes were seen in the activity of other nuclei during occlusion. These electrophysiological data provide direct evidence for a role of the PAG in the integrating neurocircuitry of the exercise pressor reflex in humans. 相似文献
157.
An integrated UASB-sludge digester system for raw domestic wastewater treatment in temperate climates 总被引:1,自引:0,他引:1
To improve the performance of an upflow anaerobic sludge blanket (UASB) reactor treating raw domestic wastewater under temperate climates conditions, the addition of a sludge digester to the process was investigated. With the decrease in temperature, the COD removal decreased from 78% at 28 °C to 42% at 10 °C for the UASB reactor operating alone at a hydraulic retention time of 6 h. The decrease was attributed to low hydrolytic activity at lower temperatures that reduced suspended matter degradation and resulted in solids accumulation in the top of the sludge blanket. Solids removed from the upper part of the UASB sludge were treated in an anaerobic digester. Based on sludge degradation kinetics at 30 °C, a digester of 0.66 l per liter of UASB reactor was design operating at a 3.20 days retention time. Methane produced by the sludge digester is sufficient to maintain the temperature at 30 °C. 相似文献
158.
Effective therapies that prevent chronic inflammation from developing into type 1 diabetes remain elusive. In this study, we show that expression of TGF-β for just 1 wk in inflamed islets of NOD mice significantly delays diabetes development. Time course studies demonstrated that the brief TGF-β pulse protects only if administered when extensive β cell destruction has occurred. Surprisingly, TGF-β-mediated protection is not linked to enhanced Foxp3(+) regulatory T cell activity or to decreased intrapancreatic presentation of islet Ags. Instead, TGF-β disables the transition of primed autoreactive CD8(+) T cells to cytotoxic effectors and decreases generation, or maintenance, of CD8(+) memory T cells within the pancreas, significantly impairing their diabetogenic capacity. 相似文献
159.
Lack of effect of somatostatin on the stimulation of hepatic glycogenolysis by epinephrine in isolated canine hepatocytes 总被引:1,自引:0,他引:1
R W Stevenson K E Steiner D R Green A D Cherrington 《Biochimica et biophysica acta》1984,804(4):414-418
The effects of somatostatin on epinephrine's ability to stimulate glucose output have been examined in hepatocytes isolated from dogs fasted overnight. Half-maximal stimulation of phosphorylase a activity and glucose output occurred at an epinephrine concentration of approx. 5 X 10(-9) M. Somatostatin at 10, 100 or 1000 ng/ml had no effect on the ability of a maximal (1 X 10(-7) M) and a submaximal (1 X 10(-8) M) dose of epinephrine to activate phosphorylase at 2 min, or to stimulate glucose output over 20 min. Since the doses of somatostatin used in the present study are up to 50-fold higher than the blood concentrations commonly found when somatostatin is used in vivo to inhibit pancreatic hormone secretion, it seems unlikely that use of somatostatin in this way would affect stimulation of hepatic glycogenolysis by epinephrine in vivo. 相似文献
160.
Haemophilia B (sixth edition): a database of point mutations and short additions and deletions. 总被引:1,自引:1,他引:1 下载免费PDF全文
F Giannelli P M Green S S Sommer M C Poon M Ludwig R Schwaab P H Reitsma M Goossens A Yoshioka G G Brownlee 《Nucleic acids research》1996,24(1):103-118
The sixth edition of the haemophilia B database lists in easily accessible form all known factor IX mutations due to small changes (base substitutions and short additions and/or deletions of <30 bp) identified in haemophilia B patients. The 1380 patient entries are ordered by the nucleotide number of their mutation. Where known, details are given on factor IX activity, factor IX antigen in circulation and origin of mutation. References to published mutations are given and the laboratories generating the data are indicated. 相似文献