全文获取类型
收费全文 | 53851篇 |
免费 | 3852篇 |
国内免费 | 135篇 |
出版年
2021年 | 388篇 |
2020年 | 336篇 |
2019年 | 371篇 |
2018年 | 875篇 |
2017年 | 835篇 |
2016年 | 1266篇 |
2015年 | 1936篇 |
2014年 | 2108篇 |
2013年 | 2697篇 |
2012年 | 3301篇 |
2011年 | 3084篇 |
2010年 | 1896篇 |
2009年 | 1448篇 |
2008年 | 2552篇 |
2007年 | 2561篇 |
2006年 | 2513篇 |
2005年 | 2361篇 |
2004年 | 2319篇 |
2003年 | 2140篇 |
2002年 | 2143篇 |
2001年 | 1552篇 |
2000年 | 1661篇 |
1999年 | 1311篇 |
1998年 | 497篇 |
1997年 | 401篇 |
1996年 | 382篇 |
1995年 | 361篇 |
1994年 | 377篇 |
1993年 | 344篇 |
1992年 | 808篇 |
1991年 | 787篇 |
1990年 | 754篇 |
1989年 | 710篇 |
1988年 | 655篇 |
1987年 | 592篇 |
1986年 | 575篇 |
1985年 | 538篇 |
1984年 | 480篇 |
1983年 | 442篇 |
1982年 | 389篇 |
1981年 | 378篇 |
1979年 | 491篇 |
1978年 | 364篇 |
1977年 | 311篇 |
1975年 | 370篇 |
1974年 | 355篇 |
1973年 | 331篇 |
1972年 | 361篇 |
1971年 | 321篇 |
1968年 | 311篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
941.
Eberhard Fuchs Jan-Christian Wasmuth Gabriele Flügge Gerald Huether Raphael Troost Jürgen Beyer 《Cellular and molecular neurobiology》1996,16(1):21-37
Summary 1. Corticotropin-releasing factor (CRF) is thought to be involved in the regulation of the diurnal activity of the hypothalamus-pituitary-adrenal
(HPA) axis and to act as a neurotransmitter in the brain. To date it is unknown whether the binding sites of the central CRF
system are subject to diurnal variations.
2. We measured the number of CRF binding sites over the course of a complete 24-hr light-dark cycle in the pituitary, amygdala,
bed nucleus of the stria terminalis (BNST), cingulate cortex, visceral cortex, paraventricular nucleus of the hypothalamus,
hippocampus, and locus ceruleus of rats byin vitro receptor autoradiography with iodinated ovine CRF. A 24-hr time course was also established for plasma CRF and corticosterone.
3. The diurnal pattern of plasma CRF does not correlate with the pattern of plasma corticosterone. Within the brain, CRF binding
in the basolateral nucleus of the amygdala showed a U-shaped curve with maximum levels in the morning and a wide hallow between
1500 and 0100. A biphasic profile with a small depression in the afternoon and a more pronounced depression in the second
half of the activity period is characteristic for the other brain areas and the pituitary. The profile for the pituitary correlates
with those for the BNST and the area of the locus ceruleus. Furthermore, the diurnal pattern of CRF binding sites in the BNST
correlates with that of the hippocampus, and the daytime pattern of the visceral cortex is similar to that of both the hippocampus
and the BNST.
4. Since the CRF-binding profiles in the brain and the pituitary clearly differ from the profiles of both plasma CRF and corticosterone,
one may assume that the diurnal pattern of central CRF binding sites is not directly coupled to the activity of the HPA axis. 相似文献
942.
High-conductance calcium-activated potassium channels; Structure,pharmacology, and function 总被引:19,自引:0,他引:19
Gregory J. Kaczorowski Hans -Günther Knaus Reid J. Leonard Owen B. McManus Maria L. Garcia 《Journal of bioenergetics and biomembranes》1996,28(3):255-267
High-conductance calcium-activated potassium (maxi-K) channels comprise a specialized family of K+ channels. They are unique in their dual requirement for depolarization and Ca2+ binding for transition to the open, or conducting, state. Ion conduction through maxi-K channels is blocked by a family of venom-derived peptides, such as charybdotoxin and iberiotoxin. These peptides have been used to study function and structure of maxi-K channels, to identify novel channel modulators, and to follow the purification of functional maxi-K channels from smooth muscle. The channel consists of two dissimilar subunits, and . The subunit is a member of theslo Ca2+-activated K+ channel gene family and forms the ion conduction pore. The subunit is a structurally unique, membrane-spanning protein that contributes to channel gating and pharmacology. Potent, selective maxi-K channel effectors (both agonists and blockers) of low molecular weight have been identified from natural product sources. These agents, together with peptidyl inhibitors and site-directed antibodies raised against and subunit sequences, can be used to anatomically map maxi-K channel expression, and to study the physiologic role of maxi-K channels in various tissues. One goal of such investigations is to determine whether maxi-K channels represent novel therapeutic targets. 相似文献
943.
Since the exact mechanism of manganese (Mn)-induced learning disability is not known, we investigated the role of elevated
cholesterol in rats exposed daily to 357 and 714 μg Mn/kg for 30 d. Significant Mn accumulation was accompanied by increased
cholesterol content in the hippocampal region of Mn-treated rats. The learning, which is based on the time needed to reach
food placed at the exit of a T-maze after a 1-d training period, was significantly slower in exposed rats than in unexposed
rats. The rats receiving 357 and 714 μg Mn/kg reached the food in 104.5±13.8 and 113.3±25.7 s, respectively, on d 30, whereas
their untreated counterparts reached the food in 28.7±11.4 s. This delay was completely corrected to 29.3±7.8 and 30.7±6.0
s in rats with coadministration of an inhibitor of cholesterol biosynthesis with 357 and 714 μg/kg of Mn. The correction of
impaired learning was associated with the normalization of hippocampal cholesterol, but the Mn level in this region of the
brain was not influenced in rats treated with a drug that inhibits cholesterol biosynthesis. These results suggested that
Mn-induced hypercholesterolemia is involved in Mn-dependent learning disability. 相似文献
944.
945.
946.
947.
Markus Kurz Karin Schütz Michael Göbel 《Origins of life and evolution of the biosphere》1996,26(3-5):263-264
948.
Summary Late Arenigian biohermal reef mounds and biostromes within the shallow-marine platform facies of the upper San Juan Formation
of the Precordillera (Western Argentina) represent a new Early Ordovician reef type. The meter-sized reefs are dominated byZondarella communis n.g. n. sp. The new taxon is characterized by domical, bulbous and laminar morphotypes exhibiting growth layers and thin
horizontal and vertical as well as intermingled skeletal elements included within different sets. The fossil maybe compared
with stromatolites and stromatoporoids but an interpretation as primitive stromatoporoids is favoured. 相似文献
949.
Summary The microproblematicumPycnoporidium ? eomesozoicum
Flügel, 1972, from Upper Triassic reefs of the Alpine-Mediterranean region, Turkey Oman and Iran (originally interpreted as possible
alga) represents the type species of a new strophomenid brachiopod genus (Gosaukammerella n.g.). The genus is characterized by a very small, millimeter-sized plano-convex shell, whose ventral valve is attached to
the substratum (mainly sponges) by symmetrically arranged outgrowths developing from a pseudopunctate, lamellose foliated
shell wall and composed of densely spaced subparallel ‘tubes’ comparable with productide spines secreted by papillose extensions
of the mantle.Gosaukammerella seems to be the only reliable candidate for the existence of post-Paleozoic strophomenid (productid ?) brachiopods.
Gosaukammerella eomesozoica is restricted to possibly cryptic, shaded reef environments inhabited predominantly by sponges serving as substrates for
micromorphic brachiopods. 相似文献
950.
Klaus Zuberbühler Lorenz Gygax Nerida Harley Hans Kummer 《Primates; journal of primatology》1996,37(1):1-12
In a captive group of long-tailed macaques, tool-using behavior by a single competent individual had a significant effect on the synchronous manipulative behavior of naïve animals. Group members engaged in manipulations on the same object class more frequently during times when the model was working than when it was not. The form of their behavior, however, in no way resembled the technique used by the model. All three animals that later became successful tool users were among the few subjects that exhibited a significant increase in manipulations on the same object class while the model was working. Possible causal relationships between this stimulus enhancement and the transmission of the new behavior to other group members are analyzed and discussed. 相似文献