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881.
882.
Pauline Schaap 《Development genes and evolution》1983,192(2):86-94
Summary The appearance and spatial distrubution of ultrastructural markers ofDictyostelium discoideum differentiation were quantitatively analysed. Our results combined with data from the literature on the functions of cells at various stages of development lead to the following conclusions. When food is no longer available all amoebae initially develop an autophagic apparatus in order to sustain metabolism. After slugs have been formed, autophagy is suppressed in the prespore cells. During aggregation a number of cells gradually form prespore characteristics. These cells arise at random but later they become located in the basal part of the tip-forming aggregate. From the early slug stage onwards, cells of the posterior two third region gradually enter into the prespore pathway. During prolonged slug migration the optimal acquirement of prespore characteristics is blocked. Cells of the anterior region show no active differentiation but they maintain the morphology and most of the functions of aggregating cells. At the rear-guard of the slug and later on in the basal region of the maturing fruiting body, a second anteriorlike region appears. Actual stalk cell differentiation takes place only at the apex and at the base of the developing fruiting body. 相似文献
883.
884.
Lewis Irving Held Jr. Christine Marie Duarte Kourosh Derakhshanian 《Development genes and evolution》1986,195(3):145-157
Summary The legs of flies from 16 different mutant strains ofDrosophila melanogaster were examined for abnormal cuticular polarities and extra joints. The strains were chosen for study because they manifest
abnormal cuticular polarities in some parts of the body (10 strains) or because they have missing or defective tarsal joints
(6 strains). All but three of the stocks were found to exhibit misorientations of either the bristles, hairs, or “bract-socket
vectors” on the legs. The latter term denotes an imaginary vector pointing from a hairlike structure called a “bract” to the
bristle socket with which it is associated. On the legs of wild-type flies nearly all such vectors point distally, as do the
bristles and hairs. In the mutant flies, the most common vector misorientation is a 180° reversal. When the bract-socket vectors
of adjacent bristle sites in the same bristle row point toward one another, the distance between the sites is frequently abnormally
large, whereas when the vectors point in opposite directions, the interval is frequently abnormally small. This correlation
is interpreted to mean that bristle cells actively repel one another via cytoplasmic extensions that are longer in the direction
of the bract-socket vector than in the opposite direction. Repulsive forces of this kind may be responsible for “fine-tuning”
the regularity of bristle spacing in wild-type flies.
Extra tarsal joints were found in eight of the 16 strains. A ninth strain completely lacking tarsal joints appears in some
cases to have an extra tibia-basitarsus joint in its tibia. Whereas the tarsi of wild-type flies contain four joints, the
tarsi ofspiny legs mutant flies contain as many as eight joints. In this extreme extra-joint phenotype, four of the joints correspond to the
normal wild-type joints, and there is an extra joint in every tarsal segment except the distal-most (fifth) segment. Nearly
all such ectopic extra joints have inverted polarity. In other strains the extra tarsal joints are located mainly at the wild-type
joint sites, and joints of this sort have wild-type polarity. The alternation of normal and inverted (extra) joints inspiny legs resembles the alternation of normal and inverted (extra) body segment boundaries in the embryonic-lethal mutantpatch, suggesting that tarsal and body segmentation may share a common patterning mechanism. 相似文献
885.
David W. Goodall 《Plant Ecology》1974,29(2):135-146
886.
本文对10名患有腹泻或肠炎的患者和10名健康者做了肠道五种优势菌群的检测,应用模式识别对两组菌群检测值进行分析。结果,图形上两组清楚地分为两处,有明显的分界线。表明,5种菌群数值在两组间具有明显差异。经评估,可知该方法平均诊断预报能力可达75%以上。 相似文献
887.
The adaptive significance of leaf-mining pattern as an anti-parasitoid strategy: A theoretical study
Makoto Katô 《Population Ecology》1985,27(2):265-275
An adaptive significance of linear leaf mining patterns as the anti-parasitoid strategy is theoretically analysed. In the model, a leaf-miner is allowed to move in one of four ways; mining ahead in unexploited area of a leaf, backtracking, branching off from the backtracking mine, and crossing the previous mine. The model parasitoid searches for the leaf-miner by tracing the mine by the tactile cue of mine surface after detecting the mine. The average duration from detecting the mine to finding the leaf-miner host is calculated for various patterns of mining, changing numbers of branches and of crosses. This average duration becomes longer when the leaf-miner stays near either end of the mine compared with when staying near its center. It is also prolonged as the numbers of branches and of crosses increase. 相似文献
888.
Despite the remarkable morphological diversity in the leaf shape, usually higher plants maintain a flat lamina to ensure the desirable surface-to-volume ratio. The control of expansion of a flattened lateral organ is only partially known and the characterization of leaf mutants can be a useful strategy to add new information, as demonstrated in dicots with recessive mutants of model species. In sunflower, the dominant mutant Basilicum Leaf (BL) is characterized by prominent downward leaf curling. The central end of the present work is the detailed study of the BL phenotype to characterize the effects of this mutation, at organ and cellular levels, on both morphological and physiological traits. The geometry of mature leaves is obviously altered in BL plants because the lamina surfaces are downward curled and display a different length/width ratio with respect to wild type. The area of BL leaves is higher than that of wild type while the BL leaf perimeter is reduced. In BL leaves, the perimeter to the square root of area ratio is also abnormally low compared to the value of a flat sunflower lamina. These results suggest that the dominant mutation induces a deep change of the ratio between lamina and marginal growth. In addition, the epidermis and mesophyll of BL leaves comprised higher size pavement and palisade cells compared to those of wild type, indicating that the BL gene also control cell shape changes in the formation of the leaf lamina. Other leaf traits such as photosynthetic pigment content, pattern of minor vein architecture, margin type and stomatal density are affected by the mutation. In BL plants, the longitudinal axis of both cotyledons and ray flower corollas shows an unusual curvature while the diameter of shoot and inflorescence meristems is reduced. In mutant leaves, the gas exchange performance is influenced by low stomata conductance while the CO2 assimilation rate is also depressed by a depleted Rubisco activity. Together, these data demonstrate the pleiotropic nature of the BL mutation, which affects a number of morphological aspects of flattened lateral organs as well as physiological parameters in sunflower. 相似文献
889.
Ki Beom Lee 《Ocean Development & International Law》2018,49(3):226-235
In November 2016, the Korea Coast Guard published the “Manual for the Use of Weapons” in response to the sometimes violent resistance of Chinese fishing vessels to the law enforcement activities of the Korea Coast Guard. This article looks at this manual, the possible uses of crew-served weapons, and the international legal precedents for the use of force at sea. 相似文献