全文获取类型
收费全文 | 10844篇 |
免费 | 2050篇 |
国内免费 | 1332篇 |
出版年
2024年 | 43篇 |
2023年 | 445篇 |
2022年 | 404篇 |
2021年 | 666篇 |
2020年 | 682篇 |
2019年 | 677篇 |
2018年 | 539篇 |
2017年 | 591篇 |
2016年 | 568篇 |
2015年 | 636篇 |
2014年 | 703篇 |
2013年 | 860篇 |
2012年 | 486篇 |
2011年 | 602篇 |
2010年 | 483篇 |
2009年 | 582篇 |
2008年 | 589篇 |
2007年 | 583篇 |
2006年 | 444篇 |
2005年 | 408篇 |
2004年 | 352篇 |
2003年 | 352篇 |
2002年 | 299篇 |
2001年 | 233篇 |
2000年 | 186篇 |
1999年 | 182篇 |
1998年 | 138篇 |
1997年 | 115篇 |
1996年 | 134篇 |
1995年 | 118篇 |
1994年 | 125篇 |
1993年 | 100篇 |
1992年 | 91篇 |
1991年 | 89篇 |
1990年 | 65篇 |
1989年 | 66篇 |
1988年 | 60篇 |
1987年 | 51篇 |
1986年 | 49篇 |
1985年 | 69篇 |
1984年 | 48篇 |
1983年 | 41篇 |
1982年 | 62篇 |
1981年 | 36篇 |
1980年 | 32篇 |
1979年 | 23篇 |
1978年 | 33篇 |
1977年 | 26篇 |
1976年 | 17篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
31.
32.
33.
Ralph G. Pearson 《Inorganica chimica acta》1998,270(1-2):252-260
A simple bonding model previously used to calculate cohesive energies is used to calculate electronic properties of simple solids. The model assumes that AB compounds of CN6 or 8 are completely ionic and that CN4 compounds, and metals, are completely covalent. It is then possible to calculate the electronic chemical potential, the work function and the average energy gap between filled and empty bands in insulators, semiconductors and conductors. 相似文献
34.
The lagena (the third otolith endorgan in vertebrates) 总被引:1,自引:1,他引:0
V. I. Khorevin 《Neurophysiology》2008,40(2):142-159
In this review, the structure and functions of the lagena (the third otolith organ) in an evolutionary lineage of the vertebrates
are described and discussed. The lagenar macula appears first in the posterior part of the sacculus of elasmobranchs; in these
animals, the lagena is considered to be involved in the balance support (orientation with respect to the gravitation force).
The lagena as a separate endorgan has been described in teleost fishes; in some species, the lagena is connected with the
sacculus, while in other species the interrelations of these structures can be dissimilar. The lagena supplements the functions
of the sacculus; in fishes (animals with no special organ of hearing), it is involved in discrimination of sound oscillations,
identification of the gravitation vector, and orientation in the course of movements within the vertical plane. In amphibians,
the lagena is localized in the posterior part of the sacculus, near the auditory structures; it performs mostly vestibular
and (to a much lesser extent) auditory functions. In amniotes, the lagena was first separated from the sacculus; it is localized
in the cochlear canal, distally with respect to the hearing organ. Information on the functions of the lagena in amniotes
is rather limited and contradictory. Central projections of this organ have been examined practically only in birds. Lagenar
afferents project to the vestibular nuclei and cerebellum, while some fibers come to the auditory nuclei of the medulla. The
lagena in birds can be related to their navigation abilities (birds are supposed to be capable of orienting within the magnetic
field of the Earth due to the magnetic properties of the lagenar otoconia; this structure can also provide detection of movements
along the vertical axis. The close proximity between the otolithic and auditory endorgans in the cochlear canal of amniotes
can be indicative of the functional significance of these interrelations. This aspect, however, remains at present undiscovered.
In mammals (except Monotremata), there is no lagena as an independent endorgan.
Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 160–178, March–April, 2008. 相似文献
35.
36.
L B Flander 《American journal of physical anthropology》1978,49(1):103-110
Metric data on 200 sacra of known sex, age and race are analyzed to determine the usefulness of conventional observations for determining sex in this bone. Results of the univariate analysis show that significant sex differences in the sacrum involve primarily the top portion of the bone for both whites and blacks. However, measurements of curvature are important sex differences in the sample of blacks. A new index relating the S1 body to sacral breadth is proposed as more useful in classifying the bones by sex than indices involving other measurements. Discriminant analysis shows that the sample of whites can be analyzed significantly better by this method than by using an index. The choice of univariate or multivariate method must depend on the condition of the bone, and will be influenced to some extent by the race from which the sample is drawn. 相似文献
37.
38.
T K Black 《American journal of physical anthropology》1978,48(1):77-82
Mesiodistal and buccolingual crown dimensions of the right deciduous teeth of 133 white children were analyzed for information on sexual dimorphism and sex discrimination using discriminant analysis. Even though consistent differences were found for only 15 out of 20 paired measurements, five of them significant at p = 0.05 or better, discriminant analysis showed the possibility of correctly sexing up to 75% of the juvenile sample, using a maximum of seven deciduous teeth. 相似文献
39.
R. Haux 《Biometrical journal. Biometrische Zeitschrift》1985,27(6):607-622
In this article a test for the comparison of K groups of independent profiles is suggested. It is based on rank tests, in which the criterion is obtained by using a suitably chosen ordinal classification function. This function represents a specific view on the profiles. The test, which is easy to use, can be regarded as a generalisation of other well known tests and can be applied within a variety of situations. The relationships to other procedures for the analysis of profiles are described. Some properties are discussed. 相似文献
40.
Flow cytometry is now being used more frequently to determine sperm functional characteristics during semen assessment for artificial insemination. With this methodology, viable and potentially functional cells are detected as unstained events differentiated from non-sperm events through their light-scattering characteristics. However, it can be shown mathematically that identification of sperm on the basis of light scatter leads to significant overestimation of unstained viable cells and underestimation of responding cells in tests of sperm function (subpopulations expressing different fluorescence patterns). We have developed a simple and cost-efficient flow cytometric approach for identifying non-sperm particles that can be carried out in parallel with functional assessments. Our method is based on the sperm's osmotic intolerance. Diluted in water, lethal osmotic shock causes major damage to the cell membranes, and all sperm will stain with propidium iodide (PI). Particulate material which is not PI-positive can then be quantitatively evaluated by FACS analysis and the results substituted in mathematical equations to provide true values for sperm counts and subpopulations. In practical tests, the percentage of non-sperm particles determined by this technique was closely comparable to the figure obtained either by SYBR14®/PI staining or by PI/CFDA staining. As well as being valuable with respect to tests of sperm function, the procedure is also suitable for obtaining accurate sperm counts during routine semen evaluation. 相似文献