全文获取类型
收费全文 | 521篇 |
免费 | 76篇 |
专业分类
597篇 |
出版年
2021年 | 4篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 13篇 |
2015年 | 18篇 |
2014年 | 17篇 |
2013年 | 21篇 |
2012年 | 18篇 |
2011年 | 30篇 |
2010年 | 10篇 |
2009年 | 5篇 |
2008年 | 16篇 |
2007年 | 17篇 |
2006年 | 14篇 |
2005年 | 18篇 |
2004年 | 14篇 |
2003年 | 15篇 |
2002年 | 23篇 |
2001年 | 20篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 4篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1960年 | 4篇 |
1939年 | 4篇 |
1934年 | 4篇 |
1932年 | 7篇 |
排序方式: 共有597条查询结果,搜索用时 15 毫秒
91.
Sul OJ Lee HW Kim WK Choi JH Kwak JS Choi YJ Latour AM Koller BH Jeong CS Kwon BS 《Biochemical and biophysical research communications》2008,367(2):277-283
TR2 (TNFR-related 2, HVEM, or TNFRSF-14), a member of the TNFR family, is involved in a number of immune responses. While TR2 is expressed on the surface of T cells during the resting state, little is known regarding how expression of the TR2 gene is regulated. To understand the mechanisms regulating the expression of TR2 in T cells, we analyzed the 5' flanking region of TR2. We identified an important region for the activity of the TR2 promoter using site directed mutagenesis. Using EMSA analysis, we found that IRF-2 was bound to the promoter region of the TR2 gene during the resting state of EL-4 T cells. Transfection of IRF-2 expression plasmid and of dominant negative IRF-2 mutant further confirmed our results. Together, these data demonstrate that IRF-2 is involved in the regulation of TR2 expression in EL-4 T cells. 相似文献
92.
C N Koller L S Bauer R M Hollingworth 《Biochemical and biophysical research communications》1992,184(2):692-699
Native crystals of Bacillus thuringiensis var. san diego, a coleopteran-specific delta-endotoxin, were metabolically labelled with [35S]methionine. Specific activity was 82,000 CPM/micrograms (2.44 Ci/mmol). Using a universal buffer formulated with the same ionic strength at every pH, we determined that native crystals dissolve above pH 10 and below pH 4. At the acidic pH, the rate of solubilization was substantially slower than at the alkaline pH. Recrystallization rates for the toxin were similar regardless of solubilization conditions. The banding patterns in denatured polyacrylamide gel electrophoresis were unaffected by solubilization conditions. Toxicity was higher for soluble toxin compared to crystal toxin, but virtually identical for the acidic and alkaline produced solutions. Acid solubilization is significant because of the acidic midgut of susceptible Coleoptera. 相似文献
93.
94.
95.
The compound, palmate lamina of Lupinus palaestinus reorients photonastically, as well as phototropically in response to non-directional and directional light signals, respectively, by structural deformations of pulvini. When the excitation provided by directional light is maintained constant (fluence rate, angle of incidence and azimuth, with respect to the leaflet laminae), the entire lamina reorients towards it at a constant angular velocity over a considerable time interval and displacement. The laminar pulvinules are considerably longer than the subtending common petiolar pulvinus and therefore contribute most to laminar reorientation. The pulvinar region is characterized by transverse folds around its circumference, and longitudinal rib-like thickenings on the external walls of its epidermis that facilitate axial and transverse deformations. Specialized “joints”, at the distal and proximal ends of each pulvinule, contribute most to its flexing. Anthocyanin is notable by its absence. Specialized “motor” tissues surrounding the central vascular core participate in pulvinar deformation by undergoing directional and differential volume changes. The bundle sheath is characterized by numerous starch grains. The multi-layered cortical parenchyma exhibits an abundance of transversely oriented primary pit fields and associated plasmodesmata. When the leaflet lamina rotates around its midrib, the pulvinus twists along its axis, exhibiting epidermal and cortical deformation. The functional significance of these specializations is discussed. 相似文献
96.
J. Kohl E. A. Koller M. Brandenberger M. Cardenas U. Boutellier 《European journal of applied physiology and occupational physiology》1997,75(4):305-311
The purpose of the present study was to investigate the effect of exercise induced hyperventilation and hypocapnia on airway
resistance (R
aw), and to try to answer the question whether a reduction of R
aw is a mechanism contributing to the increase of endurance time associated with a reduction of exercise induced hyperventilation
as for example has been observed after respiratory training. Eight healthy volunteers of both sexes participated in the study.
Cycling endurance tests (CET) at 223 (SD 47) W, i.e. at 74 (SD 5)% of the subject's peak exercise intensity, breathing endurance
tests and body plethysmograph measurements of pre- and postexercise R
aw were carried out before and after a 4-week period of respiratory training. In one of the two CET before the respiratory training
CO2 was added to the inspired air to keep its end-tidal concentration at 5.4% to avoid hyperventilatory hypocapnia (CO2-test); the other test was the control. The pre-exercise values of specific expiratory R
aw were 8.1 (SD 2.8), 6.8 (SD 2.6) and 8.0 (SD 2.1) cm H2O · s and the postexercise values were 8.5 (SD 2.6), 7.4 (SD 1.9) and 8.0 (SD 2.7) cm H2O · s for control CET, CO2-CET and CET after respiratory training, respectively, all differences between these tests being nonsignificant. The respiratory
training significantly increased the respiratory endurance time during breathing of 70% of maximal voluntary ventilation from
5.8 (SD 2.9) min to 26.7 (SD 12.5) min. Mean values of the cycling endurance time (t
cend) were 22.7 (SD 6.5) min in the control, 19.4 (SD 5.4) min in the CO2-test and 18.4 (SD 6.0) min after respiratory training. Mean values of ventilation (
E) during the last 3␣min of CET were 123 (SD 35.8) l · min−1 in the control, 133.5 (SD 35.1) l · min−1 in the CO2-test and 130.9 (SD 29.1) l · min−1 after respiratory training. In fact, six subjects ventilated more and cycled for a shorter time, whereas two subjects ventilated
less and cycled for a longer time after the respiratory training than in the control CET. In general, the subjects cycled
longer the lower the
E, if all three CET are compared. It is concluded that R
aw measured immediately after exercise is independent of exercise-induced hyperventilation and hypocapnia and is probably not
involved in limiting t
cend, and that t
cend at a given exercise intensity is shorter when
E is higher, no matter whether the higher
E occurs before or after respiratory training or after CO2 inhalation.
Accepted: 11 September 1996 相似文献
97.
98.
Tremor is commonly encountered in medical practice, but can be difficult to diagnose and manage. It is an involuntary rhythmic oscillation of a body part produced by reciprocally innervated antagonist muscles. Tremors vary in frequency and amplitude and are influenced by physiologic and psychological factors and drugs. Categorization is based on position, posture, and the movement necessary to elicit the tremor. A resting tremor occurs when the body part is in repose. A postural tremor occurs with maintained posture and kinetic tremor with movement. Various pathologic conditions are associated with tremors. Essential tremor, which is the most common, is postural and kinetic, with a frequency between 4 and 8 Hz, and involves mainly the upper extremities and head. Essential tremor responds to treatment with primidone, beta-blockers, and benzodiazepines. Parkinson''s disease causes a 4- to 6-Hz resting tremor in the arms and legs that responds to the use of anticholinergics and a combination of carbidopa and levodopa. Tremor can also be a manifestation of Wilson''s disease, lesions of the cerebellum and midbrain, peripheral neuropathy, trauma, alcohol, and conversion disorders. Treatment should be directed to the underlying condition. Stereotactic thalamotomy of thalamic stimulation is a last resort. 相似文献
99.
J R Murrell D Koller T Foroud M Goedert M G Spillantini H J Edenberg M R Farlow B Ghetti 《American journal of human genetics》1997,61(5):1131-1138
An autosomal dominant presenile dementia affecting 39 individuals in a seven-generation, 383-member pedigree has been studied at Indiana University. In the affected members of this family, clinical symptoms occurred early in life, with an average age at onset of 48.8 years. The presenting clinical features include disequilibrium, neck stiffness, dysphagia, and memory loss. As the disease progresses, further cognitive decline, superior-gaze palsy, and dystaxia also are observed. The average duration from onset of symptoms to death is approximately 10 years. Neuropathologic studies of nine affected individuals showed neuronal loss in several areas of the CNS, as well as argentophilic tau-immunopositive inclusions in neurons and in oligodendroglia. A limited genomic screen by use of DNA samples from 28 family members localized the gene for this disorder to a 3-cM region on chromosome 17, between the markers THRA1 and D17S791. The gene for tau also was analyzed, through samples from the family. 相似文献
100.
In this paper, we explore modeling overlapping biological processes. We discuss a probabilistic model of overlapping biological processes, gene membership in those processes, and an addition to that model that identifies regulatory mechanisms controlling process activation. A key feature of our approach is that we allow genes to participate in multiple processes, thus providing a more biologically plausible model for the process of gene regulation. We present algorithms to learn each model automatically from data, using only genomewide measurements of gene expression as input. We compare our results to those obtained by other approaches and show that significant benefits can be gained by modeling both the organization of genes into overlapping cellular processes and the regulatory programs of these processes. Moreover, our method successfully grouped genes known to function together, recovered many regulatory relationships that are known in the literature, and suggested novel hypotheses regarding the regulatory role of previously uncharacterized proteins. 相似文献