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71.
Relationships among several of the ion movements associated with the acrosome reaction of S. purpuratus were investigated. Egg jelly initiates 45Ca2+ and 22Na+ uptake, and K+ and H+ efflux. H+ efflux and 22Na+ uptake occur with approximately equivalent stoichiometries as rapidly as the appearance of acrosomal rods, perhaps reflecting a linked process. Most K+ loss, as measured either by 42K+ efflux or K+-ion-selective electrodes, occurs after the acrosome reaction is complete. Since an elevation of seawater K+ (from 10 to 15 mM) or the addition of 0.5 mM tetraethylammonium (TEA), an inhibitor of K+ channels, inhibits the acrosome reaction half-maximally, K+ movements or alterations of K+-dependent membrane potentials may regulate the triggering by jelly. Most, but not all, of the 45Ca2+ influx is inhibited with a mixture of 10 μM FCCP, 1 mM CN?, and 2 μg/ml oligomycin, suggesting that the mitochondria store most of the Ca2+. The extracellular Na+ concentration affects Ca2+ fluxes: sperm placed into 5 mM Na+ seawater have enhanced 45Ca2+ uptake, but do not undergo the acrosome reaction, unless 30 mM Na+ is also added. Low Na+ concentrations lead to spontaneous triggering, by allowing for both Ca2+ influx and Na+-dependent H+ efflux. At least one early Ca2+ requirement precedes the Na+ and H+ movements, as inferred from attempts at reversing the inhibitors of jelly induction of the acrosome reaction. When sperm are incubated with jelly in the absence of Ca2+, then washed and incubated with jelly in the presence of Ca2+, the acrosome reaction is triggered only upon the second incubation. However, when sperm are mixed with jelly in the presence of the other inhibitors (verapamil, TEA, 5 mM Na+ seawater, low pH, or elevated K+), they are altered so that even upon subsequent washing, jelly-mediated triggering is no longer possible. This suggests the existence of an intermediate state in the reaction pathway, that follows an event for which Ca2+ is required, but that precedes the Na+ and H+ movements, which are inhibited by all inhibitors of the acrosome reaction. These data are used to develop a partial sequence of ionic changes associated with the triggering mechanism. 相似文献
72.
Causes for the death of the eggs in the prawn Macrobrachium nobilii are: i) shedding of eggs by ovigerous female, and ii) infection by epibionts: a Saprolegnial fungus, bacteria (gram negative) and protozoans (Vorticellids and Paramecium). A cause for the death of freshly hatched larvae of some decapods is the reduction in reserve yolk energy in the larvae hatched in the last few batches. To circumvent these disadvantages, an artificial incubator was designed, in which 70% of the 3-day old eggs can successfully be incubated and hatched simultaneously. The isolted eggs are irrigated with filtered and aerated water over a diaphragm in the incubator; the water flushed from below through the diaphragm in the artificial incubator, sways and keeps the eggs continuously in a suspended motion, simulating the irrigation technique of the mother.Presented in the Second International Symposium on Invertebrate Reproduction held in Davis, California during August, 1979 相似文献
73.
Toennies Frevert 《Hydrobiologia》1980,74(1):17-28
Phosphorus release rates from profundal sediments of Lake Constance (Obersee) have been determined in D.O., pH regulated sediment-water systems. Above 10% O2 saturation (> 1.2 ppm D. O.) and with pH as in situ, no net release could be found. Sedimentations of diatom sludge (Asterionella formosa) and carbonate-phosphate coprecipitate (CaCO3.CaHPO4) increased the release to 0.5 mg × m–2 × d–1 which, however, will not be relevant to the P balance in Obersee. The annual phosphorus accumulation in profundal Obersee and Ueberlingersee is, therefore, observed as due to sinking of phosphorus-bound detritus during the stagnation period.The experimental work was carried out at the Limnological Institute of the University of Freiburg/Breisgau (West Germany) and has been supported by the Industrieverband Körperpflege und Waschmittel e.V. and the Gernan Research Council (DFG)The experimental work was carried out at the Limnological Institute of the University of Freiburg/Breisgau (West Germany) and has been supported by the Industrieverband Körperpflege und Waschmittel e.V. and the Gernan Research Council (DFG) 相似文献
74.
Contamination transferred into the uterus from external genitalia during artificial insemination (AI) has been hypothesized to cause lowered bovine pregnancy rates (PR). Using aseptic techniques, there is still a possibility of uterine contamination during routine AI. Two experiments were conducted to evaluate the effect of two types of sheath covers (CS) placed over the conventional French Medium Syringe assembly (FMS) used for AI. Their use entailed passing the assembly to the external os of the cervix, pushing the FMS through the CS and manipulating the FMS to the cervical uterine junction in the normal manner. Fifty-six day non-return rate (NRR) in dairy and actual PR in beef cattle were evaluated. In Experiment 1, 30 professional technicians were employed to inseminate 7, 387 dairy cows, while in Experiment 2, six technicians with varying levels of experience inseminated 416 beef cows. Least-squares means for NRR in dairy cattle were 78% using a CS and 79% without. Means for PR in beef cattle were 57% using a CS and 62% without. In Experiment 2, the overall PR was lower in Trial l than in other trials (P<0.05). Since some technicians improved with time, the difference due to trial was attributed to technician variation in gaining experience with a CS. Results indicate that general use of a CS in routine AI of apparently healthy cows will not increase PR. 相似文献
75.
Sang-Im Yun Byung-Hak Song Jin-Kyoung Kim Young-Min Lee 《Journal of visualized experiments : JoVE》2015,(106)
Reverse genetics, an approach to rescue infectious virus entirely from a cloned cDNA, has revolutionized the field of positive-strand RNA viruses, whose genomes have the same polarity as cellular mRNA. The cDNA-based reverse genetics system is a seminal method that enables direct manipulation of the viral genomic RNA, thereby generating recombinant viruses for molecular and genetic studies of both viral RNA elements and gene products in viral replication and pathogenesis. It also provides a valuable platform that allows the development of genetically defined vaccines and viral vectors for the delivery of foreign genes. For many positive-strand RNA viruses such as Japanese encephalitis virus (JEV), however, the cloned cDNAs are unstable, posing a major obstacle to the construction and propagation of the functional cDNA. Here, the present report describes the strategic considerations in creating and amplifying a genetically stable full-length infectious JEV cDNA as a bacterial artificial chromosome (BAC) using the following general experimental procedures: viral RNA isolation, cDNA synthesis, cDNA subcloning and modification, assembly of a full-length cDNA, cDNA linearization, in vitro RNA synthesis, and virus recovery. This protocol provides a general methodology applicable to cloning full-length cDNA for a range of positive-strand RNA viruses, particularly those with a genome of >10 kb in length, into a BAC vector, from which infectious RNAs can be transcribed in vitro with a bacteriophage RNA polymerase. 相似文献
76.
Makoto Tomimoto 《仿生工程学报(英文版)》2014,11(1):98-108
To achieve favorable Frictional Tactile Sensation (FTS) for robot and humanoid fingers, this report investigated the effects of human finger sweat on Friction Coefficient (FC) and verified the effectiveness of artificial sweat on FTS tbr a humanoid finger. The results show that the model sweat (salt and urea water faked real sweat) increases the FC of the real finger sliding on the high hygroscopic and rough surface (paper), whereas on the low hygroscopic and smooth surface (PMMA), the sweat forms a fluid film and decreases FC, restricting severe finger adhesion. Further, the film formation and capillary adhesion force of sweat were discussed. The experimental results with the artificial sweats (ethanol and water) and humanoid finger (silicone rubber skin with tactile sensors) verifies the effectiveness. The artificial sweat restricts severe adhesion (stick-slip vibration), and enhances cognitive capability of FTS. 相似文献
77.
78.
《Cell》2022,185(18):3307-3328.e19
79.
80.
A 2017 Nature report was widely touted as hailing the arrival of the artificial womb. But the scientists involved claim their technology is merely an improvement in neonatal care. This raises an under-considered question: what differentiates neonatal incubation from artificial womb technology? Considering the nature of gestation—or metaphysics of pregnancy—(a) identifies more profound differences between fetuses and neonates/babies than their location (in or outside the maternal body) alone: fetuses and neonates have different physiological and physical characteristics; (b) characterizes birth as a physiological, mereological and topological transformation as well as a (morally relevant) change of location; and (c) delivers a clear distinction between neonatal incubation and ectogestation: the former supports neonatal physiology; the latter preserves fetal physiology. This allows a detailed conceptual classification of ectogenetive and ectogestative technologies according to which the 2017 system is not just improved neonatal incubation, but genuine ectogestation. But it is not an artificial womb, which is a term that is better put to rest. The analysis reveals that any ethical discussion involving ectogestation must always involve considerations of possible risks to the mother as well as her autonomy and rights. It also adds a third and potentially important dimension to debates in reproductive ethics: the physiological transition from fetus/gestateling to baby/neonate. 相似文献