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991.
EDWARD C. McMANUS MICHAEL T. OBERDICK ASHTON C. CUCKLER 《The Journal of eukaryotic microbiology》1967,14(3):379-381
SYNOPSIS. Sulfaquinoxaline and ethopabate are 2 chemically distinct types of antagonist of PABA with anticoccidial action. Reversal experiments with PABA and synergism studies with pyrimethamine indicated that both compounds interfered with the PABA-folic acid metabolic sequence. Six pure strains of Eimeria brunetti responded differently to the 2 compounds. The strain most sensitive to ethopabate was one of 2 strains most resistant to sulfaquinoxaline. Conversely, the strain most sensitive to sulfaquinoxaline was unresponsive to the highest doses of ethopabate employed. Hypotheses to explain the differences in biological effects of the 2 compounds were considered. 相似文献
992.
993.
MICHAEL W. DICK F.L.S. DAVID L. HAWKSWORTH V.-P.L.S. 《Botanical journal of the Linnean Society. Linnean Society of London》1985,91(1-2):175-179
A synopsis of the biology of the Ascomycotina. A wide variety of classifications of the Ascomycotina has been proposed but a consensus is being reached on the main orders that it is appropriate to recognize. Most of these orders are well characterized with respect to their ecology and nutritional requirements although defined primarily on morphology. The 43 orders are displayed diagrammatically to illustrate their host and substratum requirements. This display is intended to stimulate argument and research by broadening the consideration of evolutionary pathways to include ecological and nutritional factors. It will also be of value as a teaching aid; overlays can be constructed to show additional features not treated here. 相似文献
994.
995.
The mole rat, Spalax ehrenbergi Nehring, is a complex group involving four chromosomal types of In = 52, 54, 58 and 60. These are clinally distributed from Mount Hermon in the north to the Negev in the south, covering humid, semihumid, semiarid and arid climates. Forty-seven breeding nests of Sehrenbergi were collected from 23 localities throughout the range and processed for nidicolous arthropods. A total of five species of fleas and 53 species of gamasid mites were collected. Their distribution in the investigated area has been analysed in relation to that of the chromosomal types of S.ehrenbergi. The following conclusions have been reached:(a) Only three of the species (two haematophagous gamasids and one fungivorous acarid) range across the whole investigated area, showing strong host specificity, (b) A correlation is apparent between the distribution of several nidicolous arthropods (fleas and gamasids) and the ‘54’ geographic region. This probably reflects geographical distribution rather than host specificity, (c) Palaearctic species reach their southern limit of distribution on Mount Hermon and the Golan Heights; possibly Ethiopian ones reach their northern limit in the Negev. (d) No direct correlation has been found between nidicolous arthropods and the chromosomal types of S. ehrenbergi. (e) Subjects for future investigation are outlined. 相似文献
996.
There are presently two hypotheses concerning the modulationof avian vocalizations, one holding that resonance phenomenaplay an important role, the other that modulations are sourcegenerated. A wide variety of data tend to question the formerand support the latter. The Greenewalt model is examined in the light of recent findings,many of which support its major contentions and implications.On the other hand, the model seems to have certain weaknessesin describing the interactions of pressure, tension, and membranemovement, hence the linkage of AM and FM. Mathematical expressionsof these relationships are developed. They show that the amplitudeof oscillation will vary with the magnitude of the driving pressureperturbation and with the interaction of the frequencies ofthe perturbation and the resonant frequency of the membrane.This suggests an alternative mechanism for the AM-FM linkage. Caution is advised in the development of generalized models.Although all birds may exploit certain fundamental principles,the possibility remains that a variety of techniques may beemployed. A major difference between the techniques utilizedby oscines and non-oscines is especially probable. 相似文献
997.
The successes in comparative physiology during the last 25 yearshave resulted from the study of those cellular or subcellularphenomena common to all animals, but approachable most easilyin a few model species. In contrast, complex systems comprisingmany cooperating tissues and organs are characteristic of narrowtaxa; analysis of such systems does not yield widely applicablegeneralities. An analogy between the distribution of commoditiesand products in biological systems and in marketing channelsis developed, and the function of the circulation is consideredin that context. The accumulation and assorting of productsby the flow of blood from the tissues to the collecting vesselsemerges as a particularly important role. The techniques thathave been developed for coping with man's highly complex organizationsand activities should be applicable to analogous biologicalsystems. 相似文献
998.
MARGARET F. DOCKER MICHAEL L. KENT DOMINIQUE M. L. HERVIO JASWINDER S. KHATTRA LOUIS M. WEISS ANN CALI ROBERT H. DEVLIN 《The Journal of eukaryotic microbiology》1997,44(1):55-60
ABSTRACT. Rules of zoological nomenclature, morphological data, and robosomal DNA sequence data support the validity of the genus Nucleospora , and its placement in the family Enterocytozoonidae. Although Nucleospora exhibits most of the distinguishing morophological characteristics of the family Enterocytozoonidae Cali and Owne, 1990, the distinctively different hosts (fish and humans, respectively) and sites of development (the nuclei of immature blood cells and the cytoplasm of enterocutes) supprot the placement Nucleospora and Enterocytozoon into separate genera. Ribosomal DNA sequence comparisons between Nucleospora salmonis and Enterocytozoon bieneusi showed 19.8% genetic divergece in the large and small subunit regions. Although more inter- and intrageneric divergence between the two species is sufficiently larg to deter suppression of the genus Nucleospora as a junior synonym of Enterocytozoon. A polymerase chain reaction test for the detection of N. salmonis in chinook salmon ( Oncorhynchus tshawytscha ), based on N. salmonis -specific ribosomal DNA sequence, is described. 相似文献
999.
HENRY N. MICHAEL 《American anthropologist》1974,76(2):444-445
1000.
Competitive speciation 总被引:9,自引:0,他引:9
MICHAEL L. ROSENZWEIG 《Biological journal of the Linnean Society. Linnean Society of London》1978,10(3):275-289
A new mode of speciation, competitive speciation, is suggested. It assumes that fitness is depressed by the density of a phenotype's competitors, and that the adaptive landscape of phenotypes is complex. From this it follows that some intermediate forms may be fit if and only if some extreme forms are rare or absent. Subsequent to the evolution and population growth of both extreme forms, the intermediate may disappear and homogamy evolve among each of the extremes because of disruptive selection If so, sympatric speciation has occurred and niche space has been rendered into discrete segments.
The limitations of the forces leading to competitive speciation are explored. Competitive speciation is discussed in relation to stasipatric speciation and host race formation. It may be responsible for both. Finally the rates of geographical speciation and polyploidy are compared to those of competitive speciation. The latter should be almost as fast as polyploidy and may be at the root of adaptive radiation. Unlike either polyploidy or geographical speciation, competitive speciation accelerates when species diversity declines. 相似文献
The limitations of the forces leading to competitive speciation are explored. Competitive speciation is discussed in relation to stasipatric speciation and host race formation. It may be responsible for both. Finally the rates of geographical speciation and polyploidy are compared to those of competitive speciation. The latter should be almost as fast as polyploidy and may be at the root of adaptive radiation. Unlike either polyploidy or geographical speciation, competitive speciation accelerates when species diversity declines. 相似文献