全文获取类型
收费全文 | 47215篇 |
免费 | 3842篇 |
国内免费 | 3291篇 |
出版年
2023年 | 507篇 |
2022年 | 735篇 |
2021年 | 2100篇 |
2020年 | 1517篇 |
2019年 | 1921篇 |
2018年 | 2050篇 |
2017年 | 1676篇 |
2016年 | 2174篇 |
2015年 | 2506篇 |
2014年 | 3218篇 |
2013年 | 3477篇 |
2012年 | 3965篇 |
2011年 | 3707篇 |
2010年 | 2622篇 |
2009年 | 2299篇 |
2008年 | 2631篇 |
2007年 | 2363篇 |
2006年 | 2067篇 |
2005年 | 1697篇 |
2004年 | 1595篇 |
2003年 | 1503篇 |
2002年 | 1225篇 |
2001年 | 1001篇 |
2000年 | 837篇 |
1999年 | 608篇 |
1998年 | 375篇 |
1997年 | 310篇 |
1996年 | 297篇 |
1995年 | 317篇 |
1994年 | 291篇 |
1993年 | 225篇 |
1992年 | 290篇 |
1991年 | 259篇 |
1990年 | 208篇 |
1989年 | 192篇 |
1988年 | 129篇 |
1987年 | 175篇 |
1986年 | 145篇 |
1985年 | 128篇 |
1984年 | 101篇 |
1983年 | 95篇 |
1982年 | 82篇 |
1981年 | 78篇 |
1980年 | 52篇 |
1979年 | 62篇 |
1978年 | 66篇 |
1977年 | 49篇 |
1976年 | 50篇 |
1973年 | 63篇 |
1972年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Changes in diestrous female blood plasma progesterone, estradiol, and cortisol in response to odors of urine and midventral gland secretion (MVGS) of conspecific males during different seasons have been studied in the desert hamster (Phodopus roborowskii and Djungarian hamster (P. sungorus). In desert hamster females, a statistically significant (p ?? 0.05) increase in the plasma hormonal level was observed: for progesterone in response to conspecific male MGVS in all seasons except winter, and to conspecific male urine in spring and summer; for cortisol in response to male MVGS and urine in all seasons except spring; and for estradiol in response to male MGVS in autumn. Djungarian hamster females demonstrated a statistically significant increase in the plasma progesterone level in response to conspecific male MVGS and urine in winter and summer, and no response to the estradiol and cortisol level for both odors in all seasons. The results showed important differences in the physiological response to odors of conspecific males between females of two species of dwarf hamsters. 相似文献
73.
I. G. Panova Yu. V. Markitantova N. V. Firsova O. V. Podgornyi Yu. A. Smirnova G. T. Sukhikh R. D. Zinovieva V. I. Mitashov 《Biology Bulletin》2008,35(2):121-125
The expression of β-III tubulin, a marker protein of early neuronal cells, was studied by molecular genetic and immunochemical techniques. The study was performed with the eyes of human fetuses on weeks 8.5 to 27–28 of intrauterine development. Expression of β-III tubulin was detected immunochemically in the retina and lens fibers of fetuses at stages of 8.5 to 22–23 weeks. By means of PCR, a strong expression of the β-III tubulin gene was revealed in the retina of 9.5-week fetuses. Its level remained high until week 18, became slightly lower by week 24, and decreased to zero by week 27–28. The expression of this gene was also revealed in the lens of 9.5-week fetuses. Its level at stages of 15 to 24 weeks was very low, and no expression could be detected in 27-to 28-week fetuses. The results of PCR analysis were consistent with immunochemical data. 相似文献
74.
V. K. Rybal’chenko G. V. Ostrovskaya I. V. Poralo T. V. Rybal’chenko Yu. M. Mel’nik 《Neurophysiology》1999,31(3):223-225
On modeled monolayer phospholipid (formed from azolectin) membranes, we studied the surface activity of optical isomers of
a dipeptide, kyotorphin (Tyr-Arg), and a cardiotonic agent, suphan (N-succinyltryptophan potassium salt). It was found that
the membranotropic activity of four studied isomers of kyotorphin is distributed in the order: LL>DL≈LD>DD, and two isomers
(by tryptophan) of suphan as LL>DL. The data obtained suggest that the primary mechanism underlying binding of kyotorphin
and suphan to the plasma membrane can be considered based on interaction of their molecules with the molecules of membrane
phospholipids. Binding of molecules of kyotorphin and suphan by the lipid matrix to the plasma membrane and/or their incorporation
into the matrix is a result of the above interaction. 相似文献
75.
Tong Xie Linda Yu Martin W Bader James C A Bardwell Chang-An Yu 《The Journal of biological chemistry》2002,277(3):1649-1652
Disulfide bond (Dsb) formation is catalyzed in the periplasm of prokaryotes by the Dsb proteins. DsbB, a key enzyme in this process, generates disulfides de novo by using the oxidizing power of quinones. To explore the mechanism of this newly described enzymatic activity, we decided to study the ubiquinone-protein interaction and identify the ubiquinone-binding domain in DsbB by cross-linking to photoactivatable quinone analogues. When purified Escherichia coli DsbB was incubated with an azidoubiquinone derivative, 3-azido-2-methyl-5-[(3)H]methoxy-6-decyl-1,4-benzoquinone ([(3)H]azido-Q), and illuminated with long wavelength UV light, the decrease in enzymatic activity correlated with the amount of 3-azido-2-methyl-5-methoxy-6-decyl-1,4-benzoquinone (azido-Q) incorporated into the protein. One azido-Q-linked peptide with a retention time of 33.5 min was obtained by high performance liquid chromatography of the V8 digest of [(3)H]azido-Q-labeled DsbB. This peptide has a partial NH(2)-terminal amino acid sequence of NH(2)-HTMLQLY corresponding to residues 91-97. This sequence occurs in the second periplasmic domain of the inner membrane protein DsbB in a loop connecting transmembrane helices 3 and 4. We propose that the quinone-binding site is within or very near to this sequence. 相似文献
76.
An algorithm is proposed for extracting regulatory signals from DNA sequences. The algorithm complexity is nearly quadratic. The results of testing the algorithm on artificial and natural sequences are presented. 相似文献
77.
78.
V. V. Dvorkin N. N. Dzbanovskii P. V. Minakov N. V. Suetin A. Yu. Yur'ev 《Plasma Physics Reports》2003,29(9):789-795
Optical emission spectra from the microwave discharge plasma that is used to activate gas-phase deposition of carbon films are systematically investigated under various deposition conditions. The line emission intensities from CH and C2 radicals, which are responsible for the growth of the diamond and graphite phases, respectively, are studied as functions of the main macroparameters of the process. To find the relation between the features of the emission spectra and the composition of the films obtained, the films were examined using Raman spectroscopy and electron microscopy. It is shown that monitoring the relative intensities of the spectral lines can be used to obtain the desired type of film, in which case the state of the substrate surface and the presence of a catalyst on it also play an important role. Experiments on the deposition of carbon films in the pulsed regime of plasma excitation show the possibility of changing the phase composition of the film by varying both the pulse repetition rate and the off-duty factor. At the same average microwave power, the rate of film deposition in the pulsed regime of plasma excitation is lower than that in a continuous discharge; however, the growth rate of the graphite phase decreases insignificantly. 相似文献
79.
Echocardiography was used to study the parameters of cardiodynamics, systemic hemodynamics, left ventricular morphology and functioning, phase analysis of cardiac activity, and rheological blood properties in highly skilled expert swimmers. The relationship between different levels of blood circulation was established. A close correlation between the blood flow at rest and arterial pressure was found to contribute to the optimization of microvascular pressure and shear stress in accordance with body demands. 相似文献
80.
Yu. V. Mamkaev 《Biology Bulletin》2009,36(2):98-106
Different approaches to evolutionary interpretation of ontogenies are compared, with special emphasis on the evolutionary role of morphogenetic mechanisms (construction technologies) substantially affecting the structure of definitive forms: they largely determine the structural characteristics of organs, types of anatomical and histological systems, and specificity of symmetry of organisms and their parts. The role of cellular morphogenesis inherited from protozoan ancestors in the morphogenesis of multicellular organisms is demonstrated. Two main ways of improving morphogeneses are considered, based on epithelial morphogenesis and early determined few-celled primordia. On the one hand, the phylogenetic role of archallaxes and deviations is emphasized, these events often switching evolution to a fundamentally new direction. On the other hand, many characteristics of developmental stages are explainable by rationalization of morphogeneses and do not recapitulate ancestral forms, which should be taken into consideration in phylogenetic interpretation of embryogeneses; in particular, this applies to interpretation of axial relationships. 相似文献