全文获取类型
收费全文 | 6275篇 |
免费 | 613篇 |
国内免费 | 3篇 |
专业分类
6891篇 |
出版年
2023年 | 61篇 |
2022年 | 97篇 |
2021年 | 214篇 |
2020年 | 101篇 |
2019年 | 160篇 |
2018年 | 138篇 |
2017年 | 135篇 |
2016年 | 184篇 |
2015年 | 313篇 |
2014年 | 305篇 |
2013年 | 397篇 |
2012年 | 450篇 |
2011年 | 390篇 |
2010年 | 260篇 |
2009年 | 251篇 |
2008年 | 295篇 |
2007年 | 316篇 |
2006年 | 277篇 |
2005年 | 246篇 |
2004年 | 221篇 |
2003年 | 221篇 |
2002年 | 217篇 |
2001年 | 73篇 |
2000年 | 70篇 |
1999年 | 90篇 |
1998年 | 55篇 |
1997年 | 44篇 |
1996年 | 43篇 |
1994年 | 37篇 |
1993年 | 43篇 |
1992年 | 58篇 |
1991年 | 60篇 |
1990年 | 45篇 |
1989年 | 48篇 |
1988年 | 50篇 |
1987年 | 53篇 |
1986年 | 42篇 |
1985年 | 36篇 |
1984年 | 53篇 |
1982年 | 36篇 |
1981年 | 28篇 |
1979年 | 51篇 |
1978年 | 35篇 |
1977年 | 42篇 |
1976年 | 46篇 |
1975年 | 55篇 |
1974年 | 38篇 |
1973年 | 27篇 |
1972年 | 37篇 |
1968年 | 30篇 |
排序方式: 共有6891条查询结果,搜索用时 0 毫秒
91.
92.
93.
S. A. Jenkins J. N. Baxter M. Critchley A. N. Kingsnorth C. A. Makin S. Ellenbogen J. S. Grime J. G. Love R. Sutton 《BMJ (Clinical research ed.)》1997,315(7119):1338-1341
OBJECTIVE: To assess the efficacy of long term octreotide as adjuvant treatment to programmed endoscopic sclerotherapy after acute variceal haemorrhage in cirrhotic portal hypertension. DESIGN: Randomised clinical trial. SETTING: University hospital. SUBJECTS: 32 patients with cirrhotic portal hypertension. INTERVENTIONS: Programmed injection sclerotherapy with subcutaneous octreotide 50 micrograms twice daily for 6 months, or programmed injection sclerotherapy alone. MAIN OUTCOME MEASURES: Episodes of recurrent variceal bleeding and survival. RESULTS: Significantly fewer patients receiving combined octreotide and sclerotherapy had episodes of recurrent variceal bleeding compared with patients given sclerotherapy alone (1/16 v 7/16; P = 0.037, Fisher''s exact test), and their survival was significantly improved (P < 0.02, log rank test); this improvement was maintained for 12 months after the end of the study. Combined treatment also resulted in a sustained decrease in portal pressure (median decrease -6.0 mm Hg, interquartile range -10 to -4.75 mm Hg, P = 0.0002) compared with sclerotherapy alone (median increase 1.5 mm Hg, interquartile range 0.25 to 3.25 mm Hg), as well as a significant improvement in liver function as assessed by plasma concentrations of bilirubin, albumin, and alanine aminotransferase and by hepatocyte metabolism of aminopyrine labelled with carbon-14. CONCLUSION: Long term octreotide may be a valuable adjuvant to endoscopic sclerotherapy for acute variceal haemorrhage in cirrhotic portal hypertension. 相似文献
94.
Coloboma Hyperactive Mutant Mice Exhibit Regional and Transmitter-Specific Deficits in Neurotransmission 总被引:3,自引:1,他引:2
Jacob Raber Prashant P. Mehta Max Kreifeldt Loren H. Parsons Friebert Weiss Floyd E. Bloom Michael C. Wilson 《Journal of neurochemistry》1997,68(1):176-186
Abstract: The mouse mutant coloboma ( Cm /+), which exhibits profound spontaneous hyperactivity and bears a deletion mutation on chromosome 2, including the gene encoding synaptosomal protein SNAP-25, has been proposed to model aspects of attention-deficit hyperactivity disorder. Increasing evidence suggests a crucial role for SNAP-25 in the release of both classical neurotransmitters and neuropeptides. In the present study, we compared the release of specific neurotransmitters in vitro from synaptosomes and slices of selected brain regions from Cm /+ mice with that of +/+ mice. The release of dopamine (DA) and serotonin (5-HT) from striatum, and of arginine vasopressin and corticotropin-releasing factor from hypothalamus and amygdala is calcium-dependent. Glutamate release from and content in cortical synaptosomes of Cm /+ mice are greatly reduced, which might contribute to the learning deficits in these mutants. In dorsal striatum of Cm /+ mutants, but not ventral striatum, KCI-induced release of DA is completely blocked and that of 5-HT is significantly attenuated, suggesting that striatal DA and 5-HT deficiencies may be involved in hyperactivity. Further, although acetylcholine failed to induce hypothalamic corticotropin-releasing factor release from Cm /+ slices, restraint stress increased plasma corticosterone levels in Cm /+ mice to a significantly higher level than in +/+ mice, suggesting an important role for arginine vasopressin in hypothalamic-pituitary-adrenal axis activation. These results suggest that reduced SNAP-25 expression may contribute to a region-specific and neurotransmitter-specific deficiency in neurotransmitter release. 相似文献
95.
Impact of Growth in Benzoate and m-Toluate Liquid Media on Culturability of Pseudomonas putida on Benzoate and m-Toluate Plates 总被引:1,自引:0,他引:1 下载免费PDF全文
Pseudomonas putida grown in continuous culture on benzoate or m-toluate lost the ability to grow on benzoate or m-toluate plates. A similar effect was not seen with a glucose continuous culture. Cells carrying and expressing a TOL plasmid rapidly lost their ability to grow on benzoate solid medium. 相似文献
96.
97.
98.
C. N. Matthews R. Ludicky Jacob Schaefer E. O. Stejskal R. A. McKay 《Origins of life and evolution of the biosphere》1984,14(1-4):243-250
Cross-polarization magic-angle spinning15NMR spectra have been used to determine the composition of hydrogen cyanide polymers both before and after treatment with water. The unambiguous presence of secondary amide groups (as in peptide links) has been established by double-cross-polarization studies on the polymers synthesized from equimolar amounts of H13CN and HC15N. The NMR results are consistent with the hypothesis that the original heteropolypeptides on Earth were synthesized directly from hydrogen cyanide and water without the intervening formation of -amino acids. 相似文献
99.
Hyperpolarizing potentials in guinea pig hippocampal CA3 neurons 总被引:2,自引:0,他引:2
W. Douglas Knowles Jacob H. Schneiderman Howard V. Wheal Carl E. Stafstrom Philip A. Schwartzkroin 《Cellular and molecular neurobiology》1984,4(3):207-230
There is a bewildering variety of hyperpolarizing potentials which control activity in hippocampal pyramidal cells. These include an inhibitory postsynaptic potential (IPSP) with early and late components, voltage- and calcium-dependent potassium conductances, a voltage-dependent potassium conductance modulated by muscarinic agents (the M-current), and a complex and poorly understood afterhyperpolarization following epileptiform bursts. In hippocampal CA3 pyramidal cells, mossy fiber stimulation elicits an IPSP which is made up of two readily separable components. Using the in vitro slice preparation, we investigated the underlying ionic basis of these IPSP components and compared them to other hyperpolarizing potentials characteristic of the CA3 neurons. Intracellular recordings were obtained and then tissue was exposed to bathing medium low in chloride concentration or high in potassium concentration; the ion "blockers" EGTA (intracellular); tetraethylammonium (TEA) (intra- and extracellular), and barium and cobalt (extracellular); and the gamma-aminobutyric acid (GABA)/chloride antagonists penicillin, bicuculline and picrotoxin. 相似文献
100.
One hundred and eighteen patients with normal gastrointestinal function were randomly allocated to one of three feeding regimens in a double blind study to determine the relation between the tonicity of the diet and gastrointestinal side effects related to the diet and to evaluate the efficacy of "starter" regimens in reducing gastrointestinal side effects during enteral nutrition. Patients received a hypertonic diet with an osmolality of 430 mmol (mosmol)/kg (group 1), the same diet but with the osmolality increasing from 145 to 430 mmol/kg over the first four days (group 2), or an isotonic diet (300 mmol/kg) (group 3). All diets were prepared aseptically and administered by 24 hour nasogastric infusion. The mean daily nitrogen intake in group 1 was significantly greater (p less than 0.05) than that in both groups 2 and 3, and the mean overall daily nitrogen balance was significantly better (p less than 0.05) in group 1 than groups 2 and 3. The incidence of side effects related to the diet was similar in all three groups, but diarrhoea was significantly (p less than 0.001) associated with concurrent treatment with antibiotics. These findings show that undiluted hypertonic diet results in significantly better nitrogen intake and balance, that starter regimens reduce nutrient intake but not symptoms, and that diarrhoea is significantly related to treatment with antibiotics and not to administration of an undiluted hypertonic polymeric diet. 相似文献