全文获取类型
收费全文 | 13775篇 |
免费 | 1715篇 |
国内免费 | 3762篇 |
专业分类
19252篇 |
出版年
2024年 | 93篇 |
2023年 | 257篇 |
2022年 | 399篇 |
2021年 | 461篇 |
2020年 | 400篇 |
2019年 | 436篇 |
2018年 | 332篇 |
2017年 | 353篇 |
2016年 | 399篇 |
2015年 | 589篇 |
2014年 | 783篇 |
2013年 | 794篇 |
2012年 | 1036篇 |
2011年 | 1064篇 |
2010年 | 862篇 |
2009年 | 797篇 |
2008年 | 961篇 |
2007年 | 978篇 |
2006年 | 815篇 |
2005年 | 756篇 |
2004年 | 676篇 |
2003年 | 583篇 |
2002年 | 563篇 |
2001年 | 471篇 |
2000年 | 437篇 |
1999年 | 374篇 |
1998年 | 194篇 |
1997年 | 145篇 |
1996年 | 140篇 |
1995年 | 105篇 |
1994年 | 91篇 |
1993年 | 101篇 |
1992年 | 175篇 |
1991年 | 164篇 |
1990年 | 140篇 |
1989年 | 157篇 |
1988年 | 136篇 |
1987年 | 115篇 |
1986年 | 111篇 |
1985年 | 139篇 |
1984年 | 94篇 |
1983年 | 89篇 |
1982年 | 85篇 |
1981年 | 77篇 |
1979年 | 85篇 |
1978年 | 76篇 |
1977年 | 71篇 |
1974年 | 68篇 |
1973年 | 71篇 |
1969年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
Frank H. Gleason Steve K. Schmidt Agostina V. Marano 《Extremophiles : life under extreme conditions》2010,14(5):417-425
Zoosporic true fungi are thought to be ubiquitous in many ecosystems, especially in cool, moist soils and freshwater habitats
which are rich in organic matter. However, some of the habitats where these fungi are found may periodically experience extreme
conditions, such as soils in extremely dry, hot and cold climates, acidic and alkaline soils, polluted rivers, anaerobic soil
and water, saline soil and water, periglacial soils, oligotrophic soils, tree canopies and hydrothermal vents. It is clear
that many ecotypes of zoosporic true fungi have indeed adapted to extreme or stressful environmental conditions. This conclusion
is supported by studies in both the field and in the laboratory. Therefore, in our opinion, at least some true zoosporic fungi
can be considered to be extremophiles. 相似文献
13.
14.
W. J. Schmidt 《Zoomorphology》1943,39(3):692-705
Zusammenfassung Der kohlensaure Kalk der untersuchten Helicideneischalen — Bulimus maximus (Durchmesser der Schale 23,6 x 25,1 mm, Dicke 0,25 mm), nicht näher bestimmte Schneckeneischale aus Sta. Catharina Brazil (Durchmesser 22,5 x 16,3 mm, Dicke 0,15 mm) — ist Calcit gemäß Optik (negativ einachsiges Konoskopbild) and Meigenscher Reaktion (in Übereinstimmung mit Kellys Beobachtungen bei Bulimus oblongus). Der Phosphatgehalt der Schale ist äuBerst gering trotz reichlichen Vorkommens der KELLyschen Phosphatkörnehen; diese sind in Wirklichkeit Gaseinschüisse. Erhitzen von Schalenstiicken braunt den Kalk bei Verkohlung der organischen Substanz durch and durch ; these durchsetzt also die Calcitkristalle, in Übereinstimmung mit Kellys Erfahrungen beim Entkalken. Erhitzen his zum Verbrennen der organischen Substanz (Wiederweißwerden der Schalenstücke) hebt die Doppelbrechung auf (Umwandlung des Calciumcarbonats in -oxyd); zugleich erscheint bräunliche Trübung im durchfallenden Licht wohl infolge des Austretens der Kohlensäure.Die Mammillenschicht auf der Innenseite der Schale besteht aus einzelnen Calcitindividuen oder Gruppen von solchen; diese Kristallkörnchen wachsen (zum Teil) zu den annähernd senkrecht stehenden Prismen aus, deren optische Achse rneist gegen die Schalenfläche geneigt ist. Vor allem bei Bulimus maximus lassen die Prismen eine innere grobgeschichtete and eine äußere feinstreifige Lage unterscheiden; die erste enthält die Gaseinschliisse, die sich bei der Schneckeneischale aus Sta. Catharina Brazil bis in die Mammillen hinein finden, and von rundlicher Form sind, während she bei Bulimus maximus zum Teil spaltenartig erscheinen. An manchen Stellen der Eischale aus Sta. Catharina Brazil tragen die Mamillen an ihrem freien Ende Scheiben aus radial gestellten Kalknadeln oder Rosetten aus größeren Kristallen, die bis zur Berührung benachbarter auswachsen können. 相似文献
15.
The influence of orotic acid on post-excitatory facilitation of evoked potentials released by electric stimulation of the tooth pulp in the sensomotor cortex was studied. 15-360 min following application of 100 mg/kg orotic acid, increase in amplitude of potentials released by stimulation of the tooth pulp, reinforcement of the post-excitatory facilitation observable 5 msec after stimulation occurred. 相似文献
16.
17.
18.
In experiments with in vivo 32P-labelled nonhistone proteins of rat liver nuclei it was shown that these components are more sensitive against degradation than the mass of the nonhistone proteins. In the presence of 0.1 mM phenylmethylsulfonylfluoride and 1 mM sodium molybdate, however, they are protected against degradation. 相似文献
19.
High hydrostatic pressure applied between sperm attachment and the onset of cortical granule exocytosis will inhibit this exocytotic event in sea urchin eggs. Such pressure-treated zygotes, nevertheless, are activated and capable of development. Thus, this technique can be used as a tool to study the relationship between cortical granule breakdown and other fertilization-related responses. We have studied whether the exocytosis of cortical granules is necessary for proton efflux (acid release) to occur. Our results indicate that although Ca2+ is released while the eggs are under pressure (a prerequisite for the following events to take place), cortical granule exocytosis and acid release are pressure-sensitive and completely inhibited at pressures above 400 atm (6000 psi) and 275 atm (4000 psi), respectively. However, upon decompression, acid release is initiated which amounts to 65–70% of that seen in the unpressurized controls, suggesting that the efflux mechanism does not require cortical granule exocytosis and must result from some modification of the original plasma membrane of the egg. The remaining 30–35% of the acid release is related to cortical granule exocytosis, since it can be obtained upon induction of the cortical granule fusion 30 min later under atmospheric pressure. The initiation of acid release after decompression indicates that the efflux mechanism is not transiently turned on at fertilization, but undergoing long-term modification; the recovery of the ability to induce cortical granule fusion after fertilization under pressure suggests a refilling of cytoplasmic Ca2+ stores within this time course. 相似文献
20.
ADENOSYLMETHIONINE DECARBOXYLASE IN DEVELOPING RAT BRAIN 总被引:12,自引:7,他引:5
Adenosylmethionine decarboxylase from rat brain has been found to be similar to the same enzyme isolated from other rat tissues in regard to kinetic parameters, pH optimum, putrescine requirement, and subcellular location. Evidence is presented that pyridoxal phosphate is not the functional cofactor in enzymatic decarboxylation by the rat brain preparation. The capacity for spermidine synthesis in developing rat brain was determined by measurement of the activity of adenosylmethionine decarboxylase. The activity increased dramatically after 10 days of postnatal age. This increase occurred after the period of maximum nucleic acid synthesis, an observation which suggests that spermidine may have a role in the functional development of the brain. 相似文献