全文获取类型
收费全文 | 539542篇 |
免费 | 57499篇 |
国内免费 | 766篇 |
专业分类
597807篇 |
出版年
2021年 | 5038篇 |
2018年 | 6715篇 |
2017年 | 6357篇 |
2016年 | 8891篇 |
2015年 | 12455篇 |
2014年 | 14075篇 |
2013年 | 18847篇 |
2012年 | 22148篇 |
2011年 | 22130篇 |
2010年 | 14615篇 |
2009年 | 12973篇 |
2008年 | 18843篇 |
2007年 | 19153篇 |
2006年 | 18005篇 |
2005年 | 16713篇 |
2004年 | 16687篇 |
2003年 | 15460篇 |
2002年 | 14879篇 |
2001年 | 20834篇 |
2000年 | 20715篇 |
1999年 | 16620篇 |
1998年 | 6491篇 |
1997年 | 6299篇 |
1996年 | 6005篇 |
1995年 | 5768篇 |
1994年 | 5374篇 |
1993年 | 5323篇 |
1992年 | 13347篇 |
1991年 | 13225篇 |
1990年 | 12913篇 |
1989年 | 12355篇 |
1988年 | 11484篇 |
1987年 | 10834篇 |
1986年 | 10319篇 |
1985年 | 10082篇 |
1984年 | 8432篇 |
1983年 | 7262篇 |
1982年 | 5509篇 |
1981年 | 4952篇 |
1980年 | 4603篇 |
1979年 | 7789篇 |
1978年 | 6317篇 |
1977年 | 5582篇 |
1976年 | 5245篇 |
1975年 | 6118篇 |
1974年 | 6691篇 |
1973年 | 6519篇 |
1972年 | 5806篇 |
1971年 | 5368篇 |
1970年 | 4594篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
G L Lucas 《Plastic and reconstructive surgery》1987,80(1):92-94
Fowler's central slip tenotomy for old mallet deformity is a well-known, but apparently seldom used procedure. Although the vast majority of patients with mallet finger can be successfully treated by well-known conservative techniques, occasional patients, such as the 11 reported here, will have enough difficulty with a chronic mallet finger to warrant rebalancing of the extensor apparatus by means of central slip tenotomy. 相似文献
962.
The authors study by means of immunoperoxidase method the pattern of thyroglobulin, triiodothyronine and thyroxine distribution in 58 cases of thyroid disorders: 15 euthyroid goiters, 10 Graves' disease, 7 Hashimoto's thyroiditis, 11 folliculo-papillary carcinomas (6 primary tumors and 5 lymph node metastases), 8 follicular carcinomas, 4 anaplastic carcinomas and 3 medullary carcinomas. Thyroglobulin, triiodothyronine and thyroxine were present in most of the thyroid disorders, excepting anaplastic and medullary carcinomas. Thyroglobulin and thyroxine were localized both in the follicular epithelium and in the colloid, whereas triiodothyronine was present especially in the follicular cells. The thyroid hormones distribution in benign lesions is rather similar. In carcinomas, the pattern of thyroglobulin, triiodothyronine and thyroxine is more heterogeneous, but generally the triiodothyronine distribution is similar to that of thyroglobulin. In some carcinomas, triiodothyronine and thyroxine showed a weak or negative immunostaining. The immunoperoxidase method is a valuable tool in the study of functional disturbances in the thyroid pathology and in the diagnosis of thyroid carcinoma metastases as well. Positive thyroid hormones staining clearly indicates the thyroid origin of metastases. 相似文献
963.
S A Magder G T Daughters J Hung E L Alderman N B Ingels 《European journal of applied physiology and occupational physiology》1987,56(4):467-473
The purpose of this study was to measure the changes and rates of adaptation of left ventricular volumes at the onset of exercise. Eight asymptomatic subjects, in whom intramyocardial markers had been implanted 3-6 years previously during aortocoronary bypass surgery, exercised in the supine position at a constant workload of 73.6 W for 5 min. Six also exercised first at 16.4 W, and then against a workload which progressively increased by 8.2 W every 15 s. Cardiac volumes were measured by computer assisted analysis of the motion of the implanted markers. In the constant workload test, cardiac output increased rapidly from 5.7 +/- 1 min-1 to 10.3 +/- 1.9 1 min-1 by 2 min and then increased more slowly to 10.8 +/- 2.0 1 min-1 by 5 min. The cardiac output increase was mainly due to an increase in heart rate from 68 +/- 12 beats min-1 to 120 +/- 16 beats min-1 with minimal changes in stroke volume. The time constant for the early increase in cardiac output was 45s and for heart rate, 35s. With progressively increasing workloads, there was an almost linear increase of heart rate and cardiac output, but these increased at a slower rate than during the early phase of the constant load exercise test. In conclusion: rapid changes in cardiac output during supine exercise were produced by changes in heart rate; changes in stroke volume provided minor adjustments to cardiac output; the end-diastolic volume was almost constant. 相似文献
964.
R A Rathod L J Bhagia G L Pandya V L Katagade D J Parikh B B Chatterjee 《European journal of applied physiology and occupational physiology》1987,56(1):58-63
A preliminary survey of the few units of the small-scale glass bangle industry in Firozabad, Agra District, Uttar Pradesh, indicated that the workers were exposed to severe degrees of heat stress during various operations in the manufacturing processes. A more detailed study in eight glass bangle units was therefore undertaken to make quantitative estimates of heat stress on exposed workers in the summer season. The thermal data collected confirmed that the heat stress on the workers was severe but measurement of certain physiological indicators revealed relatively low levels of strain amongst the exposed workers. The findings could be attributable to high degrees of acclimatization, but further observations in the field supplemented by studies on simulated exposures of volunteers in a climatic chamber seem to be warranted. 相似文献
965.
The study of the cell cycle of a yeast strain made it possible to define two parameters:T, the time elapsing between the appearance of two consecutive buds on a mother cell, and Θ, the time elapsing between the
appearance of a bud and the beginning of the first mitotic cycle. The influence of these two parameters on the growth rate
of the strain is studied. 相似文献
966.
967.
L. Chaerle F. De Boever M. Van Montagu & D. Van Der Straeten 《Plant, cell & environment》2001,24(1):15-25
Pending cell death was visualized by thermographic imaging in bacterio‐opsin transgenic tobacco plants. Cell death in these plants was characterized by a complex lesion phenotype. Isolated cell death lesions were preceded by a colocalized thermal effect, as previously observed at sites infected by tobacco mosaic virus (TMV) ( Chaerle et al. 1999 Nature Biotechnology 17, 813–816). However, in most cases, a coherent front of higher temperature, trailed by cell death, initiated at the leaf base and expanded over the leaf lamina. In contrast to the homogenous thermal front, cell death was first visible close to the veins, and subsequently appeared as discrete spots on the interveinal tissue, as cell death spread along the veins. Regions with visible cell death had a lower temperature because of water evaporation from damaged cells. In analogy with previous observations on the localized tobacco–TMV interaction ( Chaerle et al. 1999 ), the kinetics of thermographic and continuous gas exchange measurements indicated that stomatal closure preceded tissue collapse. Localized spontaneous cell death could also be presymptomatically visualized in the Arabidopsis lsd2 mutant. 相似文献
968.
Three local populations from Northeast Iceland are surveyed for the occurrence of the deflecting wrinkle of the metaconid on second deciduous and first permanent lower molars. The trait occurs more frequently on dm2 than on M1, and no sexual dimorphism is found, as expected. However, the frequencies are clearly within those predicted by the Mongoloid dental complex for Mongoloid populations. It is therefore suggested that the inclusion of the deflecting wrinkle in the Mongoloid dental complex be re-evaluated, and the racial diagnostic value of the trait taken with reservation. 相似文献
969.
G Hollósi 《Acta biologica Academiae Scientiarum Hungaricae》1977,28(4):397-404
Author followed up the activity of the three enzymes involved in the catabolism of nucleic acids--acid deoxyribonulease (DNase II), alkaline ribonuclease (RNase I), and acid ribonuclease (RNase II)--in the denervated gastrocnemius and soleus muscles of rats for 28 postoperative days. The activity of both acid nucleases increased in both types of denervated muscles, compared with the respective controls. Up to the 14th postoperative day, the activity excess of both acid nucleases was more significant in the m. gastrocnemius than in the m. soleus. The RNase I ran below the control activity during the whole period in the m. soleus and up to the 14th day in the m. gastrocnemius. The role of nucleases and nuclease inhibitors in the changes of nucleic acid catabolism in neurogenic muscular atrophies is discussed. 相似文献
970.