全文获取类型
收费全文 | 88357篇 |
免费 | 6989篇 |
国内免费 | 16篇 |
专业分类
95362篇 |
出版年
2023年 | 449篇 |
2022年 | 572篇 |
2021年 | 1173篇 |
2020年 | 916篇 |
2019年 | 1078篇 |
2018年 | 1932篇 |
2017年 | 1883篇 |
2016年 | 2274篇 |
2015年 | 2684篇 |
2014年 | 3033篇 |
2013年 | 4341篇 |
2012年 | 6048篇 |
2011年 | 6202篇 |
2010年 | 3661篇 |
2009年 | 2902篇 |
2008年 | 5051篇 |
2007年 | 5042篇 |
2006年 | 4658篇 |
2005年 | 4104篇 |
2004年 | 4053篇 |
2003年 | 3676篇 |
2002年 | 3585篇 |
2001年 | 2683篇 |
2000年 | 2832篇 |
1999年 | 1858篇 |
1998年 | 953篇 |
1997年 | 729篇 |
1996年 | 786篇 |
1995年 | 712篇 |
1994年 | 694篇 |
1993年 | 631篇 |
1992年 | 884篇 |
1991年 | 834篇 |
1990年 | 740篇 |
1989年 | 685篇 |
1988年 | 651篇 |
1987年 | 640篇 |
1986年 | 556篇 |
1985年 | 643篇 |
1984年 | 632篇 |
1983年 | 570篇 |
1982年 | 511篇 |
1981年 | 460篇 |
1980年 | 407篇 |
1979年 | 481篇 |
1978年 | 424篇 |
1977年 | 401篇 |
1975年 | 452篇 |
1974年 | 397篇 |
1973年 | 380篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
91.
92.
93.
Barna Györffy 《Planta》1941,32(1):15-37
Zusammenfassung In der Mehrzahl der untersuchten Fälle (insgesamt über 1000 Einzelmessungen) wurden die osmotischen Werte der Tetraploiden niedriger gefunden als die der Diploiden, doch sind die Unterschiede im allgemeinen gering. Junge Pflanzen hatten immer niedrigere 4n-Werte; bei alten Pflanzen und bei Pflanzen unter extremen Kulturbedingungen waren aber vielfach die Werte der 4n höher. Es wird die Hypothese aufgestellt, daß niedrigere osmotische Werte der Tetraploiden den Normalzustand darstellen, daß aber die Polyploiden wie in anderen Eigenschaften, so auch in ihrer Osmotik variabler sind und unter dem Einfluß von Außen-bedingungen ihre osmotischen Werte stärker modifizieren.Unter physiologischen Zwangsbedingungen (Trockenkultur, Pfropfungen) wurde an den Tetraploiden eine unter den gegebenen Verhältnissen zweckmäßige Erhöhung ihrer osmotischen Werte über das Niveau der 2n beobachtet. Gegen Trockenklima erwiesen sich die untersuchten Tetraploiden im Vergleich mit den Diploiden resistenter.Irgendwelche artspezifischen Eigentümlichkeiten konnten im Rahmen der untersuchten Pflanzen nicht festgestellt werden.Mit 6 Textabbildungen. 相似文献
94.
For some foodstuffs, determination of the mycotoxin ochratoxin A (OTA) requires time consuming clean up by means of solid
phase extraction (SPE). Therefore a system for automated SPE was tested for cleaning up roasted coffee as a possible way of
shortening preparation time. Validation of the method in accordance to the so called “Concept '98” led to a LOD of 0.2 μg/kg
and a recovery rate of 92%. By using the described procedure with samples of roasted coffee the OTA contents varied between
the LOD and 3.4 μg/kg. This method was also used to determine ochratoxin A in liquorice roots, ginger and valerian.
Presented at the 26th Mykotoxin Workshop in Herrsching, Germany, May 17–19, 2004 相似文献
95.
96.
M. Konečná 《Zeitschrift fur angewandte Ichthyologie》2012,28(5):806-810
This study focuses on assessing the reproduction mode of an important model species for evolutionary and behavioural ecology by using digital image analysis: the European bitterling Rhodeus amarus (Bloch, 1782). Specifications of mode of reproduction were determined using oocyte size distribution, seasonal dynamics in mean oocyte diameter and total number of oocytes in ovary samples gained from April to July 2007. The rapid oocyte count was enabled by using lucia image analysis software, which also provided measurement and colour estimations of oocytes. Bitterling ovaries showed features typical for indeterminate spawners, i.e. a continuous distribution of oocyte size over the reproductive season and recruitment of new pre‐vitelogenic oocytes in the second half of the reproductive season. These results are consistent with the view that the European bitterling is a batch spawning fish with indeterminate fecundity. 相似文献
97.
Wounding of quiescent white potato tuber tissue enhances chromatin-boundprotein phosphokinase activity, which exhibits two distinctphases during wound-healing. A moderate activation of the enzymesup to 20 hr after injury is followed by a dramatic increasein activity with a peak at 50 hr. This time-course resemblesthat of chromatinbound DNA-dependent RNA polymerase with a peakin activity at about 48 hr after wounding. The kinases phosphorylateendogenous proteins as well as added histones, phosvitin andcasein. The incorporated phosphate is stable under standardassay conditions, indicating the absence of protein phosphatases.Sensitivity of the incorporated phosphate toward trypsin andalkali, but not DNase, RNase, hydroxylamine or succinic acidpoints to seryl- and threonyl-bonds and proteins as acceptormolecules. Kinases from resting tissues are only weakly stimulatedeven by 100 mM MgCl2, those from wounded tissues exhibit pronouncedMg$$-optima at 510 mM with endogenous proteins, phosvitinand casein and 50 mM MgCl2 with histones. Wounding also increasesthe sensitivity of the kinases toward p-hydroxymercuribenzoate. Chromatin preparations from both resting and wounded tissuescontain about 40 protein bands after polyacrylamide disc gelelectrophoresis. In vitro phosphorylation of these proteinsin chromatin from quiescent tissues is comparably low and uniform.Wounding induces changes in the protein and phosphorylationpattern with a general enhancement of phosphorylative capacityand preferential phosphorylation of low molecular weight proteins. (Received August 10, 1981; Accepted November 18, 1981) 相似文献
98.
99.
Susanne Berglund Bryan J. Egner Henrik Gradén Joakim Gradén David G.A. Morgan Tord Inghardt Fabrizio Giordanetto 《Bioorganic & medicinal chemistry letters》2009,19(15):4268-4273
Herein, we disclose the discovery and optimization of 2-piperidin-4-yl-acetamide derivatives as MCH-R1 antagonists. Structural investigation of piperidin-4-yl-amide and piperidin-4-yl-ureas identified 2-piperidin-4-yl-acetamide-based MCH-R1 antagonists with outstanding in vivo efficacy but flawed with high affinity towards the hERG potassium channel. While existing hERG SAR information was employed to discover highly potent MCH-R1 antagonists with minimized hERG inhibition, additional hurdles prevented their subsequent clinical exploration. 相似文献
100.