全文获取类型
收费全文 | 448885篇 |
免费 | 55699篇 |
国内免费 | 283篇 |
专业分类
504867篇 |
出版年
2018年 | 3822篇 |
2017年 | 3506篇 |
2016年 | 5458篇 |
2015年 | 8168篇 |
2014年 | 9153篇 |
2013年 | 12866篇 |
2012年 | 14839篇 |
2011年 | 14953篇 |
2010年 | 9872篇 |
2009年 | 9130篇 |
2008年 | 13049篇 |
2007年 | 13529篇 |
2006年 | 12228篇 |
2005年 | 12038篇 |
2004年 | 11806篇 |
2003年 | 11243篇 |
2002年 | 10753篇 |
2001年 | 21629篇 |
2000年 | 21757篇 |
1999年 | 17389篇 |
1998年 | 6215篇 |
1997年 | 6469篇 |
1996年 | 6296篇 |
1995年 | 5695篇 |
1994年 | 5749篇 |
1993年 | 5568篇 |
1992年 | 13646篇 |
1991年 | 12957篇 |
1990年 | 12640篇 |
1989年 | 12494篇 |
1988年 | 11159篇 |
1987年 | 10782篇 |
1986年 | 9871篇 |
1985年 | 9649篇 |
1984年 | 8181篇 |
1983年 | 7073篇 |
1982年 | 5520篇 |
1981年 | 5001篇 |
1980年 | 4649篇 |
1979年 | 7682篇 |
1978年 | 5914篇 |
1977年 | 5424篇 |
1976年 | 5061篇 |
1975年 | 5362篇 |
1974年 | 5806篇 |
1973年 | 5655篇 |
1972年 | 5099篇 |
1971年 | 4726篇 |
1970年 | 3920篇 |
1969年 | 3850篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
941.
Utilizing horseradish peroxidase as a tracer protein, it is shown that trichogen and tormogen cells have a secretory function. Protein tracer from the haemolymph enters these cells by endocytosis and is transported to the sensillum liquor cavity by transport vacuoles and multivesicular bodies. It is also suggested that closely associated pigment cells may be involved in macromolecular transport. 相似文献
942.
943.
944.
D Matthias E Engler L Will-Shahab H J Herrmann C H Becker 《Acta biologica et medica Germanica》1977,36(9):1279-1284
A 14-days' training of rats designed to adapt the animals to the procedure of blood-pressure measurement caused in the myocardium a decrease, in serum an increase in noradrenaline ( NA) content. The latter remained unchanged following 3 days of treatment with 2.5 mg depot angiotensin II (AII) but decreased by more than one-half in the myocardium of untreated animals, and increased in serum. Despite the considerable difference in myocardial NA content and blood-pressure behaviour, both trained and untrained rats showed the same morphological reactions following administration of A II. These myocardial alterations which largely correspond to the so-called epinephrine myocarditis should not therefore be due solely to NA action; rather, the involvement of A II should be considered also. 相似文献
945.
M. Zamirul Hussain John C. Belton Rajendra S. Bhatnagar 《In vitro cellular & developmental biology. Plant》1978,14(9):740-745
Organ cultures of newborn rat lungs synthesize and accumulate DNA, RNA, collagen and noncollagenous proteins almost at a linear
rate for at least 5 days. During this period the synthesis of collagen consistently exceeds the synthesis of noncollagenous
proteins in a pattern similar to neonatal lung growth in vivo. Although some morphological characteristics of lung architecture
are distorted after culture, fundamental structural similarities to lungs growing in intact animals are retained. When these
cultures are maintained in atmospheres rich in oxygen, increased collagen synthesis is observed, a response similar to that
of lungs in intact animals exposed to high oxygen concentrations in vivo. Our studies suggest that lung organ cultures may
be a suitable system for investigating the biochemical aspects of lung tissue-environmental interaction.
These studies were supported in parts by NIH Grant HL-19668, a contract (68-03-2005) from the U.S. Environmental Protection
Agency, and grants from the California Lung Association. 相似文献
946.
947.
948.
949.
950.
Two methods of measuring respiratory transfer impedance (Ztr) were compared in 14 normal subjects, from 4 to 30 Hz, 1) studying the relationship between transrespiratory pressure (Prs) and flow at the chest when varying pressure at the mouth (Ztrm) and 2) studying the relationship between Prs and flow at the mouth when varying pressure around the chest wall (Ztrw). The similarity of the two relationships was expected on the basis of a T-network model. Almost identical phase responses were obtained from the two methods. Pressure-flow ratios were slightly larger for Ztrw than for Ztrm, but differences did not exceed 2% on average in 11 of 14 subjects. When the data were analyzed with the six-coefficient model proposed by DuBois et al. (J. Appl. Physiol. 8: 587-594, 1956), similar values were found for tissue compliance and tissue inertance but slightly different values for gaseous inertance in the airways (1.97 +/- 0.35 X 10(-2) cmH2O X l-1 X s2 for Ztrw vs. 1.73 +/- 0.26 for Ztrm; P less than 0.01). Similar results were also found for total respiratory resistance but with a slightly larger contribution of airway resistance for Ztrw (64 +/- 14 vs. 57 +/- 10%; P less than 0.05). As a practical conclusion it is recommended to measure Ztrw, which is technically much easier. 相似文献