全文获取类型
收费全文 | 749971篇 |
免费 | 84823篇 |
国内免费 | 456篇 |
专业分类
835250篇 |
出版年
2018年 | 6948篇 |
2017年 | 6628篇 |
2016年 | 9142篇 |
2015年 | 11785篇 |
2014年 | 14156篇 |
2013年 | 20397篇 |
2012年 | 22685篇 |
2011年 | 23173篇 |
2010年 | 15584篇 |
2009年 | 14531篇 |
2008年 | 20465篇 |
2007年 | 21131篇 |
2006年 | 19990篇 |
2005年 | 19267篇 |
2004年 | 18994篇 |
2003年 | 18292篇 |
2002年 | 17684篇 |
2001年 | 39280篇 |
2000年 | 39445篇 |
1999年 | 30581篇 |
1998年 | 9587篇 |
1997年 | 10249篇 |
1996年 | 9504篇 |
1995年 | 8772篇 |
1994年 | 8527篇 |
1993年 | 8595篇 |
1992年 | 24325篇 |
1991年 | 23501篇 |
1990年 | 22655篇 |
1989年 | 22042篇 |
1988年 | 20455篇 |
1987年 | 19043篇 |
1986年 | 17588篇 |
1985年 | 17336篇 |
1984年 | 14090篇 |
1983年 | 11950篇 |
1982年 | 8784篇 |
1981年 | 7882篇 |
1980年 | 7538篇 |
1979年 | 13086篇 |
1978年 | 10075篇 |
1977年 | 9293篇 |
1976年 | 8317篇 |
1975年 | 9286篇 |
1974年 | 10040篇 |
1973年 | 9748篇 |
1972年 | 8785篇 |
1971年 | 8048篇 |
1970年 | 7009篇 |
1969年 | 6693篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
861.
862.
863.
864.
865.
866.
867.
The perfusion procedure described in this paper produces high quality impregnation of pig visual and somatosensory cortical neurons with a Golgi-Cox solution. Starting within 30 min after death, pig heads were perfused with a fixative solution composed of a mixture (v/v) of liquid phenol, 5%; formalin, 14%; ethylene glycol, 25%; methanol, 28%; and water, 28% for two periods of 4 hr each. After perfusion, the heads were chilled for at least 18 hr. The entire brain was removed from the skull and then placed in 10% buffered formalin, where it remained for at least 10 days before taking the blocks that were to be immersed in the Golgi-Cox solution. Three weeks spent in the Golgi-Cox solution typically produced uniform neuron impregnation. The tissue blocks were then embedded in celloidin and sectioned at 120 micron. This procedure avoids the following difficulties: Golgi-Cox methods that produced excellent results with rodent or primate tissue were unsuccessful with pig tissue, placing fresh tissue in Golgi-Cox solution resulted in incomplete neuron impregnation, and immersion fixation in 10% buffered formalin without perfusion resulted in excessive staining of glia. 相似文献
868.
869.
The seminal receptacle or spermatheca of Portunus sanguinolentus consists of two parts--an anterior glandular and a posterior chitinous part. The chitinous part continues as the oviduct, which opens on the sternite of the sixth thoracic segment. Significant morphological and histological differences were observed between the spermatheca, as well as the oviduct, of mated and unmated crabs. In mated crabs the spermatheca is much more bulging, owing to receipt of a copious supply of seminal products, and its cells are hyperactive. Further stages of ovarian development were observed as indicators of sequential changes in the spermatheca. The secretory cells gradually disintegrate by way of holocrine secretion; this results in cellular stratification and the formation of distinct furrows in the chitinous posterior part. 相似文献
870.
Jürgen Sühnel 《Bulletin of mathematical biology》1998,60(2):197-213
A possible experimental design for combination experiments is to compare the doseresponse curve of a single agent with the
corresponding curve of the same agent using either a fixed amount of a second one or a fixed dose ratio. No interaction is
then often defined by a parallel shift of these curves. We have performed a systematic study for various types of doseresponse
relations both for the dose-additivity (Loewe additivity) and for the independence (Bliss independence) criteria for defining
zero interaction. Parallelism between doseresponse curves of a single agent and those of the same agent in the presence of
a fixed amount of another one is found for the Loewe-additivity criterion for linear doseresponse relations. For nonlinear
relations, one has to differentiate between effect parallelism (parallel shift on the effect scale) and dose parallelism (parallel
shift on the dose scale). In the case of Loewe additivity, zero-interaction dose parallelism is found for power, Weibull,
median-effect and logistic doseresponse relations, given that special parameter relationships are fulfilled. The mechanistic
model of competitive interaction exhibits dose parallelism but not effect parallelism for Loewe additivity. Bliss independence
and Loewe additivity lead to identical results for exponential doseresponse curves. This is the only case for which dose parallelism
was found for Bliss independence. Parallelism between single-agent doseresponse relations and Loewe additivity mixture relations
is found for examples with a fixed doseratio design. However, this is again not a general property of the design adopted but
holds only if special conditions are fulfilled. The comparison of combination doseresponse curves with single-agent relations
has to be performed taking into account both potency and shape parameters. The results of this analysis lead to the conclusion
that parallelism between zero interaction combination and single-agent doseresponse relations is found only for special cases
and cannot be used as a general criterion for defining zero-interaction in combined-action assessment even if the correct
potency shift is taken into account. 相似文献