全文获取类型
收费全文 | 27830篇 |
免费 | 2205篇 |
国内免费 | 44篇 |
专业分类
耳鼻咽喉 | 293篇 |
儿科学 | 1012篇 |
妇产科学 | 703篇 |
基础医学 | 3829篇 |
口腔科学 | 763篇 |
临床医学 | 3049篇 |
内科学 | 5581篇 |
皮肤病学 | 554篇 |
神经病学 | 2250篇 |
特种医学 | 1052篇 |
外国民族医学 | 3篇 |
外科学 | 3926篇 |
综合类 | 406篇 |
一般理论 | 43篇 |
预防医学 | 2560篇 |
眼科学 | 461篇 |
药学 | 1789篇 |
1篇 | |
中国医学 | 36篇 |
肿瘤学 | 1768篇 |
出版年
2022年 | 216篇 |
2021年 | 491篇 |
2020年 | 352篇 |
2019年 | 541篇 |
2018年 | 599篇 |
2017年 | 473篇 |
2016年 | 493篇 |
2015年 | 567篇 |
2014年 | 767篇 |
2013年 | 996篇 |
2012年 | 1465篇 |
2011年 | 1556篇 |
2010年 | 852篇 |
2009年 | 723篇 |
2008年 | 1360篇 |
2007年 | 1422篇 |
2006年 | 1358篇 |
2005年 | 1320篇 |
2004年 | 1132篇 |
2003年 | 1132篇 |
2002年 | 978篇 |
2001年 | 799篇 |
2000年 | 771篇 |
1999年 | 643篇 |
1998年 | 275篇 |
1997年 | 247篇 |
1996年 | 250篇 |
1995年 | 255篇 |
1994年 | 240篇 |
1993年 | 212篇 |
1992年 | 604篇 |
1991年 | 568篇 |
1990年 | 510篇 |
1989年 | 493篇 |
1988年 | 457篇 |
1987年 | 408篇 |
1986年 | 373篇 |
1985年 | 440篇 |
1984年 | 326篇 |
1983年 | 290篇 |
1982年 | 188篇 |
1979年 | 229篇 |
1978年 | 207篇 |
1977年 | 159篇 |
1976年 | 164篇 |
1975年 | 166篇 |
1974年 | 177篇 |
1973年 | 210篇 |
1972年 | 173篇 |
1971年 | 157篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
J E Holden K Mori G A Dienel N F Cruz T Nelson L Sokoloff 《Journal of cerebral blood flow and metabolism》1991,11(2):171-182
The steady-state distribution volumes of glucose, 3-O-methylglucose, and 2-deoxyglucose (2DG) are known to change as the concentration of glucose in plasma ranges from hypo- to hyperglycemic values. Model estimates of the three distribution volumes were compared with distribution volume values experimentally measured in the brains of conscious rats as the concentration of glucose in plasma was varied from 2 to 28 mM. The dependence on plasma glucose concentration of the 2DG lumped constant, the factor that relates the phosphorylation rate of 2DG to the net rate of glucose utilization at unit specific radioactivity in the plasma, had been determined previously in separate series of experiments. The model was extended to incorporate this dependence of the lumped constant. In the model both the transport and the phosphorylation barriers were assumed to be single and saturable. The values of their respective half-saturation concentrations and the ratio of the two maximum velocities for glucose were assumed to be invariant over the entire range of plasma glucose concentration. Good agreement between measured and estimated values for the distribution volumes and the lumped constant was attained over the full range of plasma glucose concentration. The model estimates reflected the progressive transport limitation of the brain glucose content as plasma glucose levels were reduced to hypoglycemic values. The results also indicated that these changes should be evident in the time course of 2DG in brain following administration by bolus or continuous infusion, and thus that indexes of local lumped constant change could be derived from the time course data. 相似文献
92.
Mitochondrial function and mitochondrial DNA in a series of 64 patients suspected of having mitochondrial myopathy 总被引:1,自引:0,他引:1
C Marsac F Degoul G Bonne N Romero I Nelson M Fardeau D Fran?ois G Ponsot J P Harpey B Eymard 《Revue neurologique》1991,147(6-7):462-466
Biochemical results concerning 64 patients suspected of mitochondrial myopathies are presented. Four clinical groups were studied including 21 encephalomyopathies, 42 ocular myopathies, 8 isolated myopathies and 3 cardiomyopathies. In 26 cases, the coexistence of a normal mitochondrial DNA and a mutated mitochondrial DNA (heteroplasmy) was found (19 simple deletions, 4 multiple deletions and 3 punctual mutations) and all cases presented with ocular disorders (excepted 2 cases with MERRF). Furthermore, 1 complex I deficiency (1 ocular myopathy), 1 complex IV deficiency (1 adult encephalomyopathy type Leigh), 3 complexes I + IV deficiencies (2 cases with a cardiomyopathy and 1 familial MELAS) and 2 pyruvate (1 adult from of Leigh's encephalomyopathy) dehydrogenase deficiencies (clinically and genetically different) did not show evidence of mitochondrial DNA mutation. 相似文献
93.
Variability in hand surface representations in areas 3b and 1 in adult owl and squirrel monkeys 总被引:4,自引:0,他引:4
M M Merzenich R J Nelson J H Kaas M P Stryker W M Jenkins J M Zook M S Cynader A Schoppmann 《The Journal of comparative neurology》1987,258(2):281-296
Detailed microelectrode maps of the hand representation were derived in cortical areas 3b and 1 from a series of normal adult owl and squirrel monkeys. While overlap relationships were maintained, and all maps were internally topographic, many map features varied significantly when examined in detail. Variable features of the hand representations among different monkeys included a) the overall shapes and sizes of hand surface representations; b) the actual and proportional areas of representations of different skin surfaces and the cortical magnifications of representations of specific skin surfaces, which commonly varied severalfold in area 3b and manyfold in area 1; c) the topographic relationships among skin surface representations, with skin surfaces that were represented adjacently in some monkeys represented in locations many hundreds of microns apart in others; d) the internal orderliness of representations; e) the completeness of representations of the dorsal hand surfaces; and f) the skin surfaces represented along the borders of the hand representation. Owl monkey maps were, in general, internally more strictly topographic than squirrel monkey maps. In both species, area 3b was more strictly topographic and less variable than was area 1. The degree of individual variability revealed in these experiments is difficult to reconcile with the hypothesis that details of cortical maps are ontogenetically specified during a period in early life. Instead, we propose that differences in the details of cortical map structure are the consequence of individual differences in lifelong use of the hands. This conclusion is consistent with earlier studies of the consequences of peripheral nerve transection and digital amputation, which revealed that cortical maps are dynamically maintained and are alterable as a function of use or nerve injury in these monkeys (Merzenich et al., '83a,b, '84a; Merzenich, '86; Jenkins et al., '84; Jenkins and Merzenich, '87). 相似文献
94.
95.
96.
Fusion of genes encoding Escherichia coli heat-stable enterotoxin and outer membrane protein OmpC. 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Infection and immunity》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The OmpC outer membrane protein of Escherichia coli was used as a carrier molecule for the nonimmunogenic heat-stable enterotoxin STa. Two fragments of different lengths of the gene encoding STa were fused in vitro to the 3' terminus of the truncated ompC gene. The resulting OmpC-STa hybrid proteins could be detected by L-[35S]cysteine labeling, and they were processed and thus exported. All synthesized hybrid protein remained cell bound and was found by fractionation mainly in the periplasm. Immunoblot analysis showed that the hybrid proteins reacted in vitro both with anti-OmpC and anti-STa antibodies, and immunization of rabbits evoked an antibody response to either of these proteins. 相似文献
97.
Distortion-product emissions and auditory sensitivity in human ears with normal hearing and cochlear hearing loss. 总被引:2,自引:0,他引:2
Distortion product emissions (DPEs) at 2f1-f2 frequencies were measured in 53 human ears; 21 of them exhibited cochlear hearing loss. DPEs were obtained as a function of stimulus level (DPE growth curves) at seven frequency regions between 707 Hz and 5656 Hz. Several distinctly different shapes or patterns of DPE growth curves were observed. These included single-segment monotonic growth curves with and without saturation at moderate and high stimulus levels, diphasic growth curves with nulls at moderate stimulus levels, and non-monotonic growth curves with negative slopes at high stimulus levels. Low-level, irregularly shaped segments were more frequent in normal-hearing ears, suggestive of normal low-level active nonlinearities from the outer-hair-cell subsystem. High-level, steeply sloped segments were frequent in hearing-impaired ears, suggestive of residual nonlinearities from a cochlear partition without functional outer hair cells. The stimulus level at which the DPE could just be distinguished from the noise floor, the DPE detection threshold, demonstrated moderate positive correlations (r's from 0.50 to 0.81) with auditory thresholds when all ears, both normal and impaired, were considered together. Those correlations were not strong enough to quantitatively predict auditory thresholds with any great accuracy. However, DPE thresholds were able to predict abnormal auditory sensitivity with some precision. DPE thresholds correctly predicted abnormal auditory sensitivity 79% of the time in the present study, and up to 96% of the time in previous studies. These results suggest that DPE thresholds may prove useful for hearing screening in cases where cooperation from the subject is limited or where corroboration of cochlear hearing loss is required. Different patterns of DPE growth curves suggest underlying micro-mechanical differences between ears, but the differential diagnostic value of those patterns remains to be determined. 相似文献
98.
99.
Carl L. Nelson Sandra G. Hickmon Robert A. Skinner 《Journal of orthopaedic research》1997,15(2):249-255
Osteomyelitis was induced in the radius in 77 rabbits and confirmed by histological examination and culture. At 4 weeks, the wounds were debrided and the animals were treated with (a) fatty acid dimersebacic acid beads (a bioerodable composite) impregnated with 20% or (b) 10% gentamicin sulfate, (c) placebo beads and intramuscular gentamicin sulfate. (d) placebo beads alone, or (e) debridement only. After 4 weeks, eradication of infection was determined by histological examination and culture. Osteomyelitis was eradicated in 93% of the animals treated with the beads and 20% gentamicin, in 67% of those treated with the beads arid 10% gentamicin, in 25% of those treated with placebo beads and intramuscular gentamicin, in 7% of those treated with placebo beads alone, and in 12.5% of those treated with debridement only (p values from <0.001 to 0.02). Fatty acid dimer-sehacie acid beads with gentamicin were then implanted in noninfected rabbits, and gentamicin sulfate concentrations in bone, serum, urine, and wound exudate were measured. Gentamicin sulfate was detectable in bone for as long as 8 weeks after implantation. Levels as high as 4,746 g/ml were present in the wound exudate for the first 7 days. Levels in the serum peaked at 1.03 μg/ml. Urine levels peaked at 135 μg/ml. 相似文献
100.